Intermittent fasting: is it better or worse than just eating less?

Intermittent Fasting, or IF, is a common tactic used when a person tries to reduce the amount of food they are eating in order to lose weight (in the form of fat loss). 

It involves eating only within a set period of time. For example, only eating between 2:00pm and 8:00pm. Or eating only every other day. The method does work – as long as the person takes in fewer calories than they need to use or store.

For some people, scheduling eating will make it easier to eat less.

But if you need to stay below 2500 calories per day to lose weight, it won’t work if you eat 3000, no matter how small the eating window.

Fasting for weight loss can distract people from the core methods of losing weight (i.e. eating less and moving more) because of some other purported but non-proven effects, like increased autophagy (recycling of damaged cell material) or increased muscle growth.

So the question is: For fat loss, does a general reduction in the amount of food we eat have different effects when it’s done using IF or when we just eat less during a normal eating schedule?

A recent study compared weight loss in three groups
1)    restricted calories without fasting (eating at 75% or normal)
2)    restricted calories with alternate-day fasting (but eating at 150% every other day)
3)    non-restricted calories with alternate-day fasting (eating at 200% every other day)

The subjects were identified as “lean & healthy”, meaning a normal body mass index and free of any conditions like diabetes, high blood pressure, high cholesterol, etc.

The results? All three groups lost weight. Group 1 (non-fasting) lost the most. Group 3 lost the least.

Also, Group 1’s weight loss was 91.6% fat. Group 3’s was only 23.1%. Which means they lost 76.9% in the form of muscle.

One effect noted was that the daily physical activity of the fasting groups. Group 2, the alternate-day fasting with restricted calories, had a “significantly reduced” amount of movement.

The takeaway? It suggests that fasting in and of itself is not a magic bullet for weight loss, as compared to eating less in general.

And for those who are fasting, the reduced metabolism and lower physical activity during fasting periods may result in less fat loss than if the eating times were not restricted.

If fasting works for you and it enables you to lose fat, and it feels ‘easier’ then by all means continue to use it as one of your weight loss tools. Some people use fasting for other effects that go beyond the physical. But fasting is not a requirement for weight loss, in any sense of the term.

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Published on October 14, 2021.