At its most basic level, weight gain occurs when calorie intake exceeds calories expended. Conversely, weight loss only occurs when energy intake is less than total calories burned. Weight loss occurs when calorie intake is reduced, regardless of the percentages of fat, protein or carbohydrates eaten. Calorie intake, not carbohydrate intake, is the determinant of body fat gain or loss. At this point, the calorie content of food is literally the only food property that has ever been convincingly demonstrated to impact how much fat is carried in our bodies. This was most recently validated by a meta-analysis of 20 studies suggesting that “for all practical purposes … a calorie is a calorie” as it relates to body-fat-weight.
Studies consistently show that once heavier, heavier individuals consume and expend approximately 20%–30% more calories than lighter individuals. Studies held within tightly controlled laboratories/dormitories demonstrate that reducing calorie intake by this same number invariably causes fat losses, suggesting that higher calorie intake is required to maintain higher weights.
Weight loss happens only if our calorie intake is lower than the total number of calories we burn, but the math should not be mistaken as simply “calories in–calories out.” The math changes in predictable ways when, as discussed, the brain detects fat loss (think GateKeeper), and generates increased appetite and decreased metabolic rate to favour weight regain.
There were also no differences between groups in insulin, glucose, lipids, sleep, activity, metabolism or fat mass.
Of note, and a potential warning of harm for those considering intermittent fasting, is that the intermittent fasting group was found to lose more lean mass (muscle) than the continuous eating group.