The Latest Research On Fasting: What 9 New Studies Say About Fasting’s Effects On Fat Loss, Satiety, Insulin Resistance, & More.

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One of the prevailing themes throughout the thousands of books, blog posts, and scientific literature that have been written about diets and weight loss, that has also been consistently shown to move the dial when it comes to improving your health, is the concept of fasting—periods of time where you simply stop stuffing calories into your gaping maw.

Fasting is consistently found across religions, diets, and cultures where there's a lot of longevity. It is a topic that's worth exploring in-depth, not only because of all the physical benefits you've no doubt heard about (and will discover below), but also because it is one of the most meaningful ways you can take your spiritual disciplines practice to the next level.

I get asked questions about fasting A LOT (How do you break a fast? What's the proper day length for a fast? Can you eat calories during a fast? Does coffee break a fast? etc., etc.), so I’ve published a decent amount of content on the powerful health benefits of fasting (with all of the nitty-gritty science highlighted for you to geek out on) in the following articles and podcasts:

However, because the science of fasting is continuously evolving—and because it’s part of my job to read, analyze, and share the most recent developments and research in the world of nutrition and fitness—for today’s article, I'm going to enlighten you with some of the latest and greatest findings when it comes to compelling fasting research that has emerged over the past year or so.

Important note: While some of the studies below examined fasting's effects on women, historically, very little research on fasting has been conducted on women. To learn more about how women may respond to fasting differently than men, check out the Kion blog series The Complete Guide to Fasting for Women, Part 1 and Part 2.


What We Already Know About Fasting

Some of the proven benefits of fasting I've previously reported on include improved body composition, increased energy, appetite regulation, a healthier gut, enhanced immunity, a sharper mind, a healthier heart, a longer lifespan, disease prevention, and more self-control and willpower.

Let's recap some of these before getting into what the latest research on fasting has to say.

Improved Body Composition: Fasting for periods of 12 hours or more has been shown to improve fat oxidation and fat-burning. Fasting has also been shown to increase your body’s secretion of human growth hormone, which aids in preserving muscle and burning body fat.

More Energy: It’s been observed that all mammals tend to be active when hungry and sedentary when fed. As counter-intuitive as it might sound, energy levels tend to increase during extended fasts due to a rise in the hormone adrenaline. Humans have likely evolved this mechanism as a way to give the body a boost to go hunt down some grub when food is scarce.

Appetite Regulation: Ghrelin, known as the “hunger hormone,” is responsible for making you want to destroy that bag of greasy potato chips. Leptin, on the other hand, is the hormone responsible for telling you that you are satiated. Balancing these hormones is one of the driving factors behind appetite regulation. Fasting has been shown to regulate ghrelin, which allows leptin to normalize and appetite to balance out. (Note: Females may not experience this benefit of fasting as much as males do. More on this later.)

Gut Health: Fasting can protect your gut against the negative impacts of stress and can lead to increased microbial diversity and elevated rates of fermentation, making your gut and immune system stronger.

Immune System Health: Mouse models have shown promising results for autoimmune conditions, specifically multiple sclerosis and type 1 diabetes. It’s hypothesized that fasting prompts the body to remove and replace damaged cells and stimulate the regeneration of damaged tissue.

Brain Health: Periods of fasting can induce autophagy in your neurons, thus protecting nerve cells from degeneration. Fasting also increases the secretion of brain-derived neurotrophic factor (BDNF), which aids the growth of new nerve cells and the formation of new neural pathways that can improve brain function as a whole, specifically memory and learning.

Heart Health: Fasting has been shown to improve a number of blood lipid markers indicative of heart health, including blood pressure, cholesterol, blood sugar, insulin sensitivity, and triglycerides.

Longevity and Disease Prevention: Autophagy is a repair process in which your cells cleanse and repair themselves by removing old and damaged proteins and replacing them with new ones. This process has been associated with anti-aging, longevity, and improved metabolic health—and becomes accelerated during periods of fasting. Autophagy has major implications for longevity and anti-aging because it keeps cells young, healthy, and functioning optimally.

Improved Self-Control and Willpower: Fasting by nature is an extreme exercise in willpower. You are consciously choosing not to give in to a deep, physical desire to eat. Frequently practicing this kind of self-control through fasting can translate into other areas of life, improving self-discipline and the ability to withstand temptations and distractions that derail you from focusing on what matters in your life.


The Latest Research On Fasting

In addition to our current understanding of the benefits of fasting, there is a constantly growing body of research to delve into. While this section is titled “The Latest Research On Fasting,” one thing that's very important to understand about fasting is that there isn't only one way to do it.

The research you're about to discover explores various fasting methods such as time-restricted feeding, intermittent fasting, fasted cardio, calorie restriction, intermittent calorie restriction, and a very-low-calorie ketogenic diet. Here's a quick rundown of each of these methods:

  • Time-restricted feeding (TRF), a type of intermittent fasting (which you'll learn more about below) involves eating during a restricted window (typically an 8- to 12-hour daytime window) and fasting during the remaining 16 to 12 hours.
  • Intermittent fasting (IF) is an umbrella term that encompasses various other types of fasting, including TRF and 24-hour fasting (say dinner ends at 7 PM, eating would not resume until 7 PM the next day.) You may see terms such as intermittent fasting and TRF used interchangeably, but intermittent fasting typically involves calorie restriction, while TRF does not.
  • Fasted cardio (FC) is just what it sounds like. It involves bouts of low-intensity exercise—such as an easy swim, hike, or bike ride—in a fasted state.
  • Calorie restriction (CR) involves reducing average daily caloric intake below what is typical or habitual, without malnutrition or deprivation of essential nutrients.
  • Similar to calorie restriction is intermittent calorie restriction (ICR), which involves reducing average daily caloric intake, but intermittently (such as three days per week), and resuming food consumption as typical on the remaining days.
  • A very-low-calorie ketogenic diet (VLCKD) involves eating, you guessed it, a very low number of calories that will put you in ketosis. In the study discussed below, a VLCKD consisted of 600–800 kcal/day, less than 50 g carbohydrates from vegetables, very low lipids (10 g of olive oil per day), and approximately 0.8 – 1.2 g of protein per kilogram bodyweight.

Now, without further ado, here are 9 newly released studies, representing what the latest science is able to show us when it comes to fasting:

1. Time-Restricted Feeding Improves Glucose Tolerance

Background: This study aimed to assess the effects of 9-hour time-restricted feeding (TRF), early (TRFe), or delayed (TRFd) on glucose tolerance in men at risk for type 2 diabetes.

The study: Fifteen men (age 55 ± 3 years, BMI 33.9 ± 0.8 kg/m2) wore a continuous glucose monitor for 7 days of baseline assessment and during two 7-day TRF conditions. Participants were randomized to TRFe (8 am to 5 pm) or TRFd (12 pm to 9 pm), separated by a 2-week washout phase. Glucose, insulin, triglycerides, nonesterified fatty acids, and gastrointestinal hormone incremental areas under the curve were calculated following a standard meal on days 0 and 7 at 8 am (TRFe) or 12 pm (TRFd).

The results: TRF improved glucose tolerance as assessed by a reduction in glucose incremental area under the curve (P = 0.001) and fasting triglycerides (P = 0.003) on day 7 versus day 0. However, there were no mealtime by TRF interactions in any of the variables examined. There was also no effect of TRF on fasting and postprandial insulin, nonesterified fatty acids, or gastrointestinal hormones. Mean fasting glucose by continuous glucose monitor was lower in TRFe (P = 0.02) but not TRFd (P = 0.17) versus baseline, but there was no difference between TRF conditions.

Overall, these results suggest that, while only TRFe lowered mean fasting glucose, TRF improved glycemic responses to a test meal in men at risk for type 2 diabetes regardless of the clock time that TRF was initiated.

Key takeaway: If you track your blood glucose and struggle with seeing numbers that are higher than ideal, eating all of your meals in an early (8 am-5 pm), compressed 9-hour window may help. If numbers that fluctuate more than you'd like are your main concern, simply try compressing your feeding window into 9 hours, beginning whenever works best for your schedule.

Check out the study here.

2. Intermittent Fasting Reduces Weight and Fat Mass and Improves Total and LDL Cholesterol

Background: This study aimed to compare intermittent fasting (IF) versus continuous energy intakes at 100% or 70% of calculated energy requirements on insulin sensitivity, cardiometabolic risk, body weight, and composition.

The study: Eighty-eight overweight women (50 ± 1 years, BMI 32.3 ± 0.5 kg/m2) were randomized to one of four diets (IF70, IF100, dietary restriction [DR70], or control) in a 2:2:2:1 ratio for 8 weeks. Intermittent fasting groups fasted for 24 hours after breakfast on three nonconsecutive days per week. All foods were provided and diets matched for macronutrient composition (35% fat, 15% protein, 50% carbohydrate). Insulin sensitivity by hyperinsulinemic-euglycemic clamp (a method for quantifying how sensitive tissue is to insulin), weight, body composition, and plasma markers were assessed following a “fed” day (12-hour fast) and a 24-hour fast (IF only).

The results: The IF70 group displayed greater reductions in weight, fat mass, total- and low-density lipoprotein cholesterol, and nonesterified fatty acids compared with DR70 and IF100 (all P ≤ 0.05). The IF100 group lost more weight and fat than control. However, fasting insulin was increased. There were no group differences in insulin sensitivity by clamp. However, a 24-hour fast transiently reduced insulin sensitivity.

Overall, these results suggest that, when prescribed at matched energy restriction, IF reduced weight and fat mass and improved total and low-density lipoprotein cholesterol more than DR. Intermittent fasting prescribed in energy balance did not improve health compared with other groups, despite modest weight loss.

Key takeaway: Although cholesterol is not necessarily a sufficient factor for predicting heart disease, intermittent fasting at 70% of your usual caloric intake for three days per week can help you lose fat and improve your metabolic health, especially if you struggle with resistance to weight loss.

Check out the study here.

3. Fasted Cardio Has a Surprisingly Satiating Effect

Background: At rest, omission of breakfast lowers daily energy intake, but also lowers energy expenditure, attenuating any effect on energy balance. The effect of breakfast omission on energy balance when exercise is prescribed is unclear. The aim of this study was to assess the effect on 24-hour energy balance of omitting, compared with consuming, breakfast prior to exercise.

The study: Twelve healthy physically active young men (age 23 ± 3 y, body mass index 23.6 ± 2.0 kg/m2) completed 3 trials in a randomized order (separated by >1 week): a breakfast of oats and milk (431 kcal; 65 g carbohydrate, 11 g fat, 19 g protein) followed by rest (BR); breakfast before exercise (BE; 60 min cycling at 50 % peak power output); and overnight fasting before exercise (FE). The 24-h energy intake was calculated based on the food consumed for breakfast, followed by an ad libitum lunch, snacks, and dinner. Indirect calorimetry with heart-rate accelerometry was used to measure substrate utilization and 24-h energy expenditure.

The results: The 24-hour energy balance was -400 kcal (normalized 95% CI: -230, -571 kcal) for the FE trial; this was significantly lower than both the BR trial (492 kcal; normalized 95% CI: 332, 652 kcal) and the BE trial (7 kcal; normalized 95% CI: -153, 177 kcal; both P < 0.01 compared with FE). Plasma glucose utilization in FE (mainly representing liver glucose utilization) was positively correlated with energy intake compensation at lunch (r = 0.62, P = 0.03), suggesting liver carbohydrate plays a role in post-exercise energy-balance regulation.

Overall, these results suggest that performing low-intensity exercise in a fasted state does not result in complete energy compensation later in the day. In healthy men, pre-exercise breakfast omission creates a more negative daily energy balance and could therefore be a useful strategy to induce a short-term energy deficit.

Key takeaway: If you're someone who struggles with the munchies and appetite cravings during the workday, fasted cardio in the morning can help with this. You don't have to kill yourself doing something like a HIIT workout, either. In this study, a leisurely, one-hour bicycle ride (50% peak power output) was all it took for results. To amplify the fat loss effects of fasted cardio, cap it off with a cold shower or plunge. This is my potent “strike, shiver, stroll” fat loss technique I outline in this article.

Check out the study here.


4. Intermittent Fasting Has Positive Effects on Decreasing Fat Mass

Background: Intermittent fasting (IF) has been studied in athletes during Ramadan and in those willing to decrease adiposity while maintaining or increasing lean body mass. The purpose of this systematic review was to summarize the effects of Ramadan IF on performance outcomes.

The study: A search of peer-reviewed articles in the following databases: PubMed, Web of Science, and Sport Discus (up to December 2019). Studies were selected if they included samples of adults (≥18 years), had an experimental or observational design, investigated IF (Ramadan and time-restricted feeding (TRF)), and included performance outcomes. Meta-analytical procedures were conducted when feasible. Twenty-eight articles met the eligibility criteria.

The results: Overall, the existent research examining the effects of IF on physical parameters and body composition has provided conflicting data. Meta-analytic findings reveal significant pooled estimate effects of IF on VO2max.

Overall, these results suggest that Ramadan IF may have some positive effects on decreasing body mass and fat mass. While Ramadan IF may lead to impairments in aerobic capacity, TRF may be effective for improving it.

Key takeaway: While Ramadan IF (fasting from dawn to sunset for one month) can help you with losing fat, it may also lead to impairments in aerobic capacity. TRF—which, as mentioned earlier does not involve calorie restriction but simply compressing your feeding into a specified window of time—may be an effective way to avoid such impairments.

Check out the study here.

5. Calorie Restriction Stimulates a Meaningful Reduction in Weight and Promotes Aging-related Benefits

Background: The Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy Phase 2 (CALERIE) study showed that individuals who are non-obese were able to undergo significant calorie restriction (CR), yet the time-course changes in adherence, weight, and appetite are unknown. This analysis aimed to investigate the time-course changes in adherence, body weight, and appetite during the CALERIE study.

The study: Overall, 143 participants (body mass index: 21.9-28.0 kg/m2) were randomized to a CR group that aimed to achieve 25% CR for 2 years. Throughout the intervention, body weight was measured, and appetite was assessed through visual analogue scales. Algorithms were utilized with bodyweight measurements to calculate adherence percentile score. Participants targeted an adherence percentile score of 50, though being between 80 (lowest acceptable adherence) and 10 (highest acceptable adherence) was adequate. Polynomial regression analyses were used to assess time course changes.

The results: Polynomials indicated that adherence percentile score increased above 50 after approximately week 20, although adherence remained acceptable (adherence percentile score less than 80) (R2 = 0.89; P < 0.001). Weight loss occurred until approximately week 60 and then plateaued (R2 ≥ 0.92; P < 0.001). Hunger and thirst increased (R2 ≥ 0.30; P < 0.001), but the total increase in scale scores were <10 mm throughout the intervention.

Overall, these results suggest that, in individuals who are nonobese, adherence to 25% CR declines after 20 weeks, but 2 years of CR that stimulates a meaningful reduction in weight, promotes aging-related benefits, and negligibly affects appetite is viable.

Key takeaway: While the scientific community has not fully accepted one single complete theory of aging, the aging-related benefits of CR may have something to do with the fact that CR reduces metabolic rate, which, in turn, decreases the rate of free radical damage in your body. Calorie restriction is also thought to result in lower levels of protein and DNA damage, thereby slowing down the aging process and allowing you to live longer with less risk of age-related diseases. Living longer sounds great and all, but if it means being hungry all the time and potentially nutrient-deficient, it kind of loses its appeal. So, if you are going to experiment with CR, be sure to fill in any nutritional gaps with supplements; i.e., if you're cutting meat out of your diet a few days per week, supplement with essential amino acids.

Check out the study here.

6. An Earlier Fast Start Time Results in a Reduced Likelihood Of Becoming Obese

Background: Circadian rhythms play an important role in the regulation of eating and fasting, and mistimed dietary intakes may be detrimental to metabolic health. Extended overnight fasting has been proposed as a strategy to better align the eating-fasting cycle with the internal circadian clock, and both observational and experimental studies have linked longer overnight fasting with lower body weight. However, it remains unclear if the timing of overnight fasting modifies the relationship between fasting duration and weight outcomes.

The study: Dietary intake of 495 men and 499 women, age 50-74 years was assessed over 12 months by 24-h dietary recalls every two months, and BMI was measured at the beginning, middle, and end of the study. Logistic regression was used to estimate the relationship between overnight fasting duration and the likelihood of being overweight.

The Results: Among participants with early overnight fasting (midpoint < 02:19 am), a longer fasting duration was associated with lower odds of overweight and obesity; while among those with late fasting (≥02:19 am), longer fasting was associated with higher odds of overweight and obesity. Specifically, when compared to the shortest quintile of overnight fasting duration, the longest quintile was associated with a 53% reduction in the odds of overweight and obesity in the early fasting group (OR = 0.47, 95% CI = 0.23, 0.97), but a 2.36-fold increase in the late fasting group (OR = 3.36, 95% CI = 1.48, 7.62). Additionally adjusting for dietary intakes during morning and late evening periods did not affect the observed associations.

Overall, these results suggest that longer overnight fasting was associated with a reduced likelihood of being overweight or obese, but only among those with an early timing of fasting.

Key takeaway: If you're looking to lose weight, starting your fast earlier (for a 12-hour fast, a midpoint before 2:19 am would put your ideal start time somewhere around 8 am) is more effective than starting later in the day.

Check out the study here.

7. A Very-Low-Calorie Ketogenic Diet Promotes Weight Loss and Reductions in Visceral Adipose Tissue and Liver Fat Fraction

Background: Currently, the treatment of non-alcoholic fatty liver disease (NAFLD) is based on weight loss through lifestyle changes, such as exercise combined with calorie-restricted dieting. This study aimed to assess the effects of a commercially available weight loss program based on a very-low-calorie ketogenic diet (VLCKD) on visceral adipose tissue (VAT) and liver fat content compared to a standard low-calorie (LC) diet. As a secondary aim, researchers evaluated the effect on liver stiffness measurements.

The study: Patients were randomized and treated either with an LC or a VLCKD and received orientation and encouragement to physical activity equally for both groups. VAT, liver fat fraction, and liver stiffness were measured at baseline and after 2 months of treatment using magnetic resonance imaging. Paired t-tests were used for comparison of continuous variables between visits and unpaired test between groups. Categorical variables were compared using the χ2-test. Pearson correlation was used to assess the association between VAT, anthropometric measures, and hepatic fat fraction. A significance level of the results was established at p < 0.05.

The results: Thirty-nine patients (20 with VLCKD and 19 with LC) were evaluated at baseline and 2 months of intervention. Relative weight loss at 2 months was −9.59 ± 2.87% in the VLCKD group and −1.87 ± 2.4% in the LC group (p < 0.001). Mean reductions in VAT were −32.0 cm2 for VLCKD group and −12.58 cm2 for LC group (p < 0.05). Reductions in liver fat fraction were significantly more pronounced in the VLCKD group than in the LC group (4.77 vs. 0.79%; p < 0.005).

Overall, these results suggest that patients undergoing a VLCKD achieved superior weight loss, with significant VAT and liver fat fraction reductions when compared to the standard LC diet. The weight loss and rapid mobilization of liver fat demonstrated with VLCKD could serve as an effective alternative for the treatment of NAFLD.

Key takeaway: This study was conducted on obese individuals under professional supervision. Long-term carbohydrate deprivation can have significant negative impacts on your hormones and electrolyte balance. If you're going to go on a keto diet, it’s important to add sufficient sodium to your diet and stay well-hydrated—especially in your first few days of starting to reduce carbohydrates. You should also incorporate “carb re-feeds” into your diet, which look something like this:

  • Eat zero net carbs the entire day until post-workout feeding (typically 1-3 hours after a 30-60 min workout that falls sometime between 4:30 and 6:30 pm).
  • Re-feed with starches up to 150-200g from sources such as millet, sweet potato, yam, white rice, red wine, dark chocolate, etc.
  • Intermittent fast for 12-16 hours; then rinse, wash, and repeat.

Check out the study here.

8. Intermittent Calorie Restriction Reduces Triglycerides and Improves Insulin Resistance

Background: Intermittent calorie restriction (ICR) is a novel method of dietary restriction for bodyweight control with the potential to improve obesity-related cardiometabolic markers, but the impact of this diet on subjects with hypertriglyceridemia (HTG) remains unknown.

The study: Eighty-eight overweight or obese subjects with mild-to-moderate HTG were randomized to either a continuous calorie restriction (CCR) group, or a very low-calorie diet during 3 days of the week (ICR) group for 8 weeks (44 patients in each group). Body composition, plasma lipids, glucose, insulin, adiponectin, and liver enzymes were measured at baseline and after 8 weeks. An intention-to-treat analysis was performed.

The results: Bodyweight decreased in both groups (4.07 ± 1.83 kg in the CCR group and 4.57 ± 2.21 kg in the ICR group) with no significant difference between the groups. There was no significant difference between the two groups in the reduced amount of fat mass, fat-free mass, and waist circumference. Both groups achieved a significant reduction in plasma triglycerides after 8 weeks (by 15.6 and 6.3% in ICR and CCR groups, respectively) with no difference between treatment groups. HOMA-IR improved significantly in ICR compared to the CCR group (P = 0.03). Plasma glucose, insulin, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, liver enzyme, and adiponectin were not different between the two groups.

Overall, these results suggest that three days a week of ICR is comparable to a CCR diet for the reduction of triglycerides level in patients with HTG, and in the short-term, it appears to be more effective than continuous dieting for improving insulin resistance.

Key takeaway: For lowering triglycerides and improving insulin resistance, ICR (consuming 30% of your daily caloric requirement for three days) is comparable to CCR (consuming 30% of your daily caloric requirement all seven days of the week). To keep track of heart health, we've all been instructed to pay attention to cholesterol, but one of the best indicators of your risk for heart disease is actually your triglyceride-to-HDL ratio—what's known as the atherogenic index of plasma (AIP). The lower your triglyceride-to-HDL ratio, the less likely you are to suffer from a cardiac event. Improving insulin resistance is also important as AIP values are directly correlated with insulin resistance.

Check out the study here.

9. Intermittent Fasting Is a Feasible Weight Loss Strategy to Improve Metabolic Syndrome

Background: The aim of this study was to determine the efficacy of an energy restriction intermittent fasting diet in metabolic biomarkers and weight management among adults with metabolic syndrome.

The study: Seventy metabolic syndrome patients, aged 18–65 years, at an academic institution were randomized to intermittent energy restriction (IER) and continuous energy restriction (CER) groups. Biochemical tests including lipid profile, fasting plasma glucose, insulin, glycosylated hemoglobin Type A1c (HbA1c), homeostatic model assessment of insulin resistance (HOMA-IR), blood pressure, and body composition were evaluated at baseline and at the 12th week in diet interviews. Dietary intake was measured with the 24-hour dietary recall method and dietary quality was evaluated with the Healthy Eating Index-2010

The results: Changes in body weight (≈7% weight loss) and composition were similar in both groups. Blood pressure, total cholesterol, triglyceride, low-density lipoprotein (LDL), fasting glucose, and insulin at the 12th week decreased in both groups (p < 0.05). No significant differences were observed in metabolic syndrome biomarkers between the IER and CER groups. The energy-restricted intermittent fasting diet did not cause any deficiencies in macronutrient and fiber intake in the subjects. Healthy Eating Index (HEI) index scores were achieved similarly in both groups, and subjects’ dietary intakes were close to daily reference nutritional intake values

Overall, these results suggest that intermittent fasting is a feasible weight loss strategy to improve metabolic syndrome and it is well tolerated. Moreover, the diet does not appear to cause an unbalanced nutritional intake. The technique used to achieve energy restriction, whether intermittent or continuous, appears to alleviate the metabolic syndrome biomarkers activated by weight loss.

Key takeaway: Metabolic syndrome is a cluster of conditions (high blood pressure and blood sugar, excess visceral fat, and abnormal cholesterol or triglyceride levels) that occur together and increase your risk of heart disease, stroke, and type 2 diabetes. As you learned in the aforementioned studies, fasting (IF in particular) can help bring down high blood pressure and sugar, reduce fat, and lower cholesterol and triglyceride levels.

Check out the study here.


Summary

I hope this overview of the latest research on fasting has enlightened you on some of the many benefits of fasting, intermittent fasting, fasted cardio, and beyond—and that it can serve as a guide for making an educated decision about which type of fasting is right for you.

To recap,

  • Time-Restricted Feeding Improves Glucose Tolerance – Eating all of your meals within a 9-hour window can improve glycemic variability. Or, better yet, an earlier (8 am-5 pm) 9-hour window can lower your fasting glucose.
  • Intermittent Fasting Reduces Fat Mass and Improves Total and LDL Cholesterol Intermittent fasting at 70% of your usual caloric intake, three days per week can help you lose fat and improve your metabolic health, especially if you struggle with resistance to weight loss.
  • Fasted Cardio Has a Surprisingly Satiating Effect – A leisurely, one-hour bicycle ride at 50% of your peak power output can keep you feeling more satiated throughout the day.
  • Ramadan IF's Positive Effects on Decreasing Fat Mass – Fasting from dawn to sunset for one month can help you with losing fat, but it may also lead to impairments in aerobic capacity. TRF may be an effective way to avoid such impairments.
  • Calorie Restriction Stimulates a Meaningful Reduction in Weight and Promotes Aging-related Benefits – By reducing metabolic rate and protein and DNA damage, CR may slow down the aging process and allow you to live longer with less risk of age-related diseases
  • An Earlier Fast Start Time Results in a Reduced Likelihood Of Becoming Obese – Starting a fast earlier (around 8 am) is more effective for fat loss than starting later in the day.
  • A Very-Low-Calorie Ketogenic Diet Promotes Weight Loss and Reductions in Visceral Adipose Tissue and Liver Fat Fraction – While a VLCKD can promote weight loss, long-term carbohydrate deprivation can have significant negative impacts on your health. If you're going to go on a ketogenic diet, it’s important to add sufficient sodium to your diet, stay well-hydrated, and incorporate “carb re-feeds.”
  • Intermittent Calorie Restriction Reduces Triglycerides and Improves Insulin Resistance – Intermittent Calorie Restriction is just as effective as continuous calorie restriction for lowering triglycerides and improving insulin resistance.
  • Intermittent Fasting Is a Feasible Weight Loss Strategy to Improve Metabolic Syndrome – Intermittent fasting can help bring down high blood pressure and sugar, reduce fat, and lower cholesterol and triglyceride levels—all markers of metabolic syndrome.

Finally, as a “last-minute addition” bonus to this fasting article…

…I was recently reading Examine Research Digest (one of my favorite, fast ways to stay up-to-date on handy summaries of the latest nutrition and exercise research), and came across a review of a study by and interview with Jeffrey Rothschild, the author of a new paper entitled “What Should I Eat before Exercise? Pre-Exercise Nutrition and the Response to Endurance Exercise: Current Prospective and Future Directions.”

The entire article is well worth a read, but in the interview within the research digest, Jeffrey replies to two particularly intriguing questions on fasting and exercise, namely:

Q. The review also mentions that, in general, being fasted or fed has a larger effect on performance than the size or timing of meals, and that fed exercise seems to be better for performance. Is there any evidence that individuals who are accustomed to training in a fasted state have less of a dip in performance?

A. The key thing here is likely to be the exercise duration. During shorter-duration exercise (less than 60 minutes), a placebo/belief effect is more likely to occur, and it could be possible for people to ‘convince’ themselves that their performance will suffer. For longer duration exercise, glycogen depletion becomes more of the issue and so I don’t think being accustomed to training fasted will help very much, presuming we’re talking about high-intensity exercise performance. There may be some mental benefit for people who are more used to the feeling of being a bit hungry, but I’m not sure how much that would affect things. I’m not sure there is a study testing this exactly, but in my research there hasn’t been any influence of habitual fasted training practices on performance in the fed vs. fasted state.

Q. What might mediate the improvement in time-to-fatigue seen in fasted athletes?

A. That was seen in one study that found better improvements in time-to-fatigue at 85% VO2max in trained cyclists performing four weeks of sprint interval training in the fasted state compared to those that consumed carbohydrate before and during exercise. In this case, I suspect it might be more to do with carbohydrate blunting the training adaptations, as opposed to fasted training improving it to an additional degree. To clarify, there seems to be the potential for carbohydrates to negatively impact training adaptations when consumed in very high amounts (and I think the amount is the key thing). In that study, the sprint training consisted of four to seven 30-second sprints, performed three times per week for four weeks. So it was a very low volume of exercise. The carbohydrate group consumed a very large amount of carbs both before and during exercise (2.5 grams per kilogram of bodyweight before, and sipping on sports drink during, training sessions). So it’s possible that the huge amount of carbs consumed before exercise (about 200 grams) could have blunted some intracellular signaling in response to the training and blunted some of the adaptations. However, I wouldn’t expect to see that result if the carb group had consumed something more modest like 50–75 grams before exercise. There’s also the confounding factor of consuming the carb drink during exercise, which can influence things on its own.

Here also is a very helpful graphic from the original interview, which you can grab with an Examine Research Digest subscription here:

 

 

So there you have it. Ultimately, please remember, fasting is a practice, which means there’s no right or wrong way to do it. The key is tuning in to your body, making adequate preparations, and finding a style that works for you.

For help with all of this, there's nothing out there that beats—in terms of comprehensive education and support—the annual Kion Fasting Challenge, which just so happens to be kicking off very soon!

Whether you're a seasoned fasting pro and just want the support of other like-minded individuals to better your physical, mental, and spiritual health; are brand new to fasting and still have some questions and concerns about starting your practice; or are somewhere in between, this challenge is for you!

Last year, we had over 10,000 people start 2020 with a five-day fast—undertaking everything from a fasting-mimicking diet to an intermittent fasting protocol, to a strict five-day water fast. So, if you’re ready to experience firsthand how you can start your year with more energy, a healthier body, a clearer mind, and an enlightened spirit, then you won't want to miss this challenge

You can sign up for the Kion Fasting Challenge today for free by clicking here.

When you register, you'll receive Kion's comprehensive fasting guide, Fasting Decoded, for free. The challenge starts on January 11th, but I highly recommend you sign up today because you’ll need to prepare yourself beforehand. (Fasting Decoded also contains an entire section on how to prepare for a fast!)

How about you? Have you fasted before? Did you struggle with it, or see good results? Leave your comments, questions, and thoughts on fasting below, and I'll respond!


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7 thoughts on “The Latest Research On Fasting: What 9 New Studies Say About Fasting’s Effects On Fat Loss, Satiety, Insulin Resistance, & More.

  1. Deon says:

    Hi Ben,

    Deon here

    This was an interesting and well-presented article, I’ve enjoyed reading every single word because the article gives value and it is broken down into sections to make it easier to digest everything. Keep doing a great job, Ben.

    I am also in the health industry, my role is to provide advice on health-related issues that people encounter on a day to day basis and I provide information that inspires and motivates people about today’s top trends in Weight loss, bodybuilding, fitness, exercise, and diets. I would be happy to share my articles with you. Thank you.

    https://deonsfitnessblog.com/exercise-fitness/what-are-the-best-types-of-aerobic-exercises/

  2. Mark says:

    HI Ben,

    Great post and super helpful! Would you mind making a comment on the merits/demerits of the 16:8 IF fasting with bullet-proof coffee (coconut/MCT oil + GF butter)?

  3. Sona says:

    Hey,
    In your Mindvalley longevity quest, you prescribed a lot of workouts. Can you tell for each of these which should be done in a fasted state and which ones in a non-fasted one? The workouts for which I want to know are-
    1. Tabata
    2. Foam rolling
    3. Core foundation
    4. Big 5
    5. Isometric routine
    6. Yoga
    7. Plank routine

  4. Robert Stambolija says:

    Dear Ben,
    Why you don’t do podcast with Dr Nun Amen Ra,
    He is way ahead regarding all this (he talk about If CR cardio etc before 8 years ago, and he has so many thing to teach you)
    I think will be a great benefit for you and your listeners hear his knowledge and research and noup he is not a quack just so head away from majority of you guys regarding biohacking
    Sincerely yours from Croatia
    Robert

  5. Joe says:

    Hey Ben, do you have any thoughts on the study that Chris Kresser recently mentioned about TRF causing a decrease in lean muscle mass? This totally goes against what Dr. Rhonda Patrick has stated with research in mice, but this was with humans.

  6. Sam says:

    Why was water only fasting not included?

  7. Clayton Carroll says:

    I have been doing time restricted eating for about 6 months now and do 5:30 am workouts in a fasted state almost every day during the week. It’s interesting because the first few mins are terrible but then my stomach evens out as my GI tract shuts down operations. Haven’t noticed a performance increase or decrease and can’t say I’ve really felt any positive effects but the research is solid. Fasting is similar to cold plunging, mind over body.

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