Update On The Safety And Efficacy Of Intermittent Fasting

I recently came across 3 new studies that examined the safety and efficacy of intermittent fasting as a weight loss strategy. I thought a quick summary of these articles would make for a nice post since I get so many questions on fasting from my clients.

Study #1

In this first study, 81 overweight subjects were randomized to one of two groups. One group consumed a normal calorie reduced diet. The other consumed the same diet, but restricted eating to a 10 hour window. After 39 weeks, there were no differences in the amount of weight lost. In other words, intermittent fasting resulted in no more weight loss than eating your meals spaced out normally (Reference 1).

Study #2

In this cross-sectional study, 1,047 older adults had their diets assessed by means of a food frequency questionnaire. Blood was also taken and cardiovascular disease biomarkers were measured. Longer fasting time was associated with lower HDL cholesterol, higher potassium levels and lower chloride levels. Although many believe that fasting improves cardiovascular disease risk factors, these are mildly detrimental associations (Reference 2).

Study #3

In this trial, 139 obese subjects were randomized to one of two groups:

-A time restricted eating group that limited food consumption to the hours of 8:00 AM and 4:00 PM.

-A normal calorie restricted group.

Each group had a goal of 1200 calories per day for the women and 1500 calories for the men. After 12 months, there was no significant difference in weight loss between the two groups (Reference 3).

Conclusions And Recommendations

The evidence is really starting to mount that intermittent fasting is not an effective or even a healthy way to lose weight. 

These studies, and other included in previous blog posts have shown that:

-Fasting is no more effective for weight loss than a more conventional, 3 meal a day approach.

-Fasting can have a negative impact on HDL and LDL cholesterol.

-Fasting can have a negative impact on blood glucose regulation.

-Fasting can have a negative impact on inflammation.

-Fasting increases hunger.

-Fasting has been shown to decrease metabolic rate, so you burn fewer calories in a day that you fast.

-Fasting has been shown to lower levels of physical activity.

-Fasting has been shown to have a negative impact on sleep.

-It is harder to adhere to a fasting protocol than a 3 meal a day plan.

-Fasting may lead to an increase in muscle loss.

If you want to see some of the research quoted above, click on this link.

From my viewpoint, enough research has accumulated to conclude that fasting is not the way to go if you want to lose weight, reduce your risk of chronic disease and/or improve your quality of life.

Three, spaced out meals a day is the best option to help you lose weight, keep your blood sugar stable for all day energy and will allow you enough eating opportunities to make sure you are getting adequate fiber, vitamins, minerals and phytochemicals.

References

1) Thomas EA, et al. Early time restricted eating compared with daily caloric restriction: A randomized trial of adults with obesity. Obesity 2022; 30:1027-38.

2) Estrada-DeLeon DB, et al. Association of prolonged nightly fasting with cardiovascular, renal, inflammation, and nutritional status biomarkers in community dwelling older adults. American Journal of Clinical Nutrition 2022; 115:1282-1289.

3) Liu D, et al. Calorie restriction with or without time restricted eating in weight loss. New England Journal of Medicine 2022; 386:1495-504.