This week, we examine whether intermittent fasting is superior for both fat loss and health when compared to a typical calorie restricted diet.

It’s hypothesized that fasting imparts health related benefits such as improved cardiovascular health and insulin sensitivity.

These health benefits are suggested to be independent of weight loss and a calorie restricted diet – i.e., fasting offers additional benefits via fasting mediated mechanisms.

However, there’s very minimal evidence that explores extended fasting and its ability to fully initiate these mechanisms (>24 hour fasting).

Therefore, Templeman et al (2021) investigated this by placing lean individuals into three groups for 3 weeks:

Group 1: Diet every day – 25% calorie deficit.
Group 2: Alternate day fasting – 24 hour fast followed by 150% of calorie intake.
Group 3: Alternate day fasting – 24 hour fast followed by 200% of calorie intake.

Essentially, groups 1 and 2 consumed the same calories over the course of the week and were in the same 25% calorie deficit to facilitate fat loss. Where group 3 consumed maintenance intake by eating more on ‘feeding’ days and therefore would not expect to see any losses in body fat…

As expected, this happened. Group 1 and 2 dropped bodymass, where group 3 maintained.

However, group 1’s weight loss was achieved almost entirely by body fat, where group 2 was close to a 50:50 loss of fat and muscle.

From a metabolic perspective, group 2 experienced a drop in compensatory energy expenditure in the afternoon and in the morning of the 150% feed which could explain the difference in body fat loss despite the same weekly calorie intake.

On fasting days, the absence of calories and protein most likely accelerated muscle mass loss (catabolic environment that favours muscle breakdown which is more pronounced in the lean).

Lastly, there was no significant difference in cardiometabolic health either.

Ultimately, a strong obvious benefit for alternate day fasting is lacking, especially in lean individuals, and especially in athletes (just no). A traditional approach appears best.

Perhaps some utility resides for obese individuals with cardiometabolic issues, but not for the former who are lean and healthy.