On the surface, intermittent fasting (IF) and caloric restriction appear similar, and both may result in the same number of calories consumed weekly. However, the differences in hormonal response, effects on metabolism, and long-term sustainability make IF a significantly better option for almost all health goals.
IF is simply cycling periods of eating with periods of fasting. We have a natural fast daily during sleep, and IF is a process the human body handles well. IF has existed throughout human history, from natural periods of food scarcity to observing religious occasions.
Most diets and literature focus on reducing calories as a means of achieving weight loss and better health. The idea that the body gains and loses weight in a calories-in/calories-out balance is very familiar. While correct in a sense, the body is not a closed chain, so other variables will impact the caloric numbers. Our system fights for homeostasis. Things like metabolic rate, core temperature, and even energy derived from food are not static numbers, and can be adjusted up and down to maintain balance.
Over time, restricting calories will cause your metabolism to drop. In order to lose more weight, calories will have to be further restricted, resulting in a downward spiral to severe metabolic slowdown. Eventually, the diet becomes too difficult to continue, and weight gain occurs quickly because of the reduced rate of energy use. Most people will feel like they have failed because of a lack of willpower, when really it was an impossible goal from the outset.
Oddly enough, the negative effects of “starvation diets” don’t happen with actual periods of starvation, only with caloric restriction. The difference is in the hormonal response.
When the body is in a fasted state, the metabolism actually goes up (shown by Resting Energy Expenditure below), and other markers are well maintained.
Growth hormone production is increased significantly. Insulin is able to be kept low over long periods because of the breaks in glucose consumption, a key for both fat loss and diabetes prevention. Over a 6 month period, insulin level improvements were doubled on an IF diet. In addition, IF improves the rate of fat loss, limits the amount of muscle loss (and can often even result in muscle gain when paired with strength training because of the increased growth hormone), and promotes the anti-aging and general health benefits of cell autophagy (the destruction and recycling of poorly functioning cells).
CER - Caloric Restriction
IER - Intermittent Fasting
Int J Obes (Lond). 2011 May; 35(5): 714–727
In short, it is preferable to eat less often, instead of less food per meal. The body will respond to fewer meal times by accessing fat stores that the steady eater will never reach. Limiting your feeding window to 6-8 hours a day is likely enough to see significant benefits, especially when paired with a low-carb or ketogenic diet.