Intermittent Fasting for Weight Loss but Overall Health Benefits May be Limited

What exactly is meant by intermittent fasting and is it a better way to lose weight than more traditional diets that are basically forms of calorie restriction?

The term "intermittent fasting" can potentially be used to describe many different types of dieting but in the clinical setting this type of dieting generally refers to three main forms. These three forms are alternate day fasting (ADF), time-restricted eating (TRE) and the 5:2 diet.

I have discussed the results of several publications on the benefits of ADF and TRE:

EFFECTS OF INTERMITTENT FEEDING IN THE APPETITE CONTROL CENTER OF THE BRAIN (HYPOTHALAMUS)

BENEFITS OF TIME RESTRICTED EATING IN PATIENTS WITH METABOLIC SYNDROME

TIME RESTRICTED FEEDING AS A MEANS TO CONTROL OBESITY?

What differentiates these three types of intermittent fasting diets from each other?

Alternate day fasting, as the name implies, involves eating one day and fasting the next, repeating over and over. In some examples of ADF diets the fasting day involves only the consumption of water, referred to as a zero calorie alternate day. There are some versions of ADF that involve consuming calories on the fast day but only up to 25% of caloric need. This latter version of ADF is referred to as modified alternate day fasting. Evidence has shown that individuals who consume this 25% or less calorie restriction all at once or throughout the day with no differences in weight loss. Therefore, the method of choice is often whichever works best for the individual. On the days of eating in the ADF diet there are no caloric restrictions.

The distinction of the time restricted eating (TRE) diet plan is that individuals are restricted to eating at specific times during the day. The eating time frame is usually four to eight hours with the remaining time spent drinking only water or zero calorie fluids. In most successful forms of the TRE consuming calories is restricted to be accomplished prior to 4pm to 6pm.

The 5:2 diet is similar in methodology to the ADF diet except that individuals eat normally for five days and then fats for two day. During the fasting days, consumption is restricted to between 500 and 1,000 kilocalories (kcal) per day.

So what do randomized controlled trials (RCT) in a clinical setting find as to the efficacy of these types of intermittent fasting diets with respect to weight loss and health outcomes?

The primary findings that are of particular interest are that when utilized for a short time frame of 8-12 weeks the ADF and 5:2 diets result in a similar level of weight loss that is generally in the range of 4% to 8% from the individuals weight at the beginning of the intermittent fasting. However, when these two forms of intermittent fast were monitored for longer periods, 24-52 weeks, there was no observed increase in weight loss. These types of results indicate that the ADF and 5:2 diets are effective only for short durations. This fact would likely lead to frustration in individuals due to the lack of continued weight loss. The degree of weight loss with the TRE diet is found to be less (3% to 4% weight loss from diet onset weight) than the ADF and 5:2 diets. Whether there is benefit to the TRE with longer term adherence is yet to be borne out by controlled trials.

When utilizing the ADF or 5:2 diets for longer periods of time some study results indicate that adherence is increased if individuals are allowed to consume slightly higher calories (for example 1,000 to 1,200 kcal per day instead of the normal 500 kcal or less) on the fasting days.

One of the biggest problems with intermittent fasting diets is that many individuals assume they can eat any amount of calories on the days they can eat and thus end up over eating on those days negating most, if not all, of the benefits of the diet. This seems to be especially true with individuals utilizing the TRE diet plan.

Aside from their weight loss benefits for what would be considered unhealthy individuals, intermittent fasting also results in up to 0.5 pounds (0.2 kilograms) per day of weight loss in individuals who are of healthy weight with no other pathological conditions.

However, despite the benefits of intermittent fasting diets with respect to weight loss, the clinical data seems to indicate that these diets may not result in significant health benefits at the level of blood pressure, blood lipid profiles, and regulation of blood glucose. Although several studies have found that intermittent fasting leads to reductions in serum triglyceride levels, this result is not observed in all studies.

An excellent review of clinical trials of the various forms intermittent fasting was recently published in the prestigious journal, Nature Reviews: Endocrinology"

Clinical application of intermittent fasting for weight loss: progress and future directions

TAKE HOME: There is ample evidence of the benefits of intermittent fasting diets with respect to weight loss. Part of the effect of these types of diets is exerted within the appetite control centers of the brain. However, in order to get real measurable health benefits from intermittent fasting it is likely that greater control needs to be exerted over the composition of the calories, not just the calories themselves.