Each time you eat a meal, your metabolism, or more specifically metabolic rate, increases. That's because all the processes for digestion and absorption require energy and blood flow. Since increasing your metabolic rate means expending energy and generating heat, this phenomenon is called the 'thermic effect of food.

More recently this viewpoint, studies suggests a protocol that calls for the individual to fast for an extended period of time (usually 16 – 18 hr) and then eat their remaining calories within a given window that usually follows an exercise. This is commonly known as intermittent fasting and has gained a lot of popularity over the past 10 – 15 years, both from fitness enthusiasts and researchers alike. Within the concept of intermittent fasting there are multiple different fasting protocols, most of which are aimed at reducing bodyweight.

One such popular protocol entails complete fasting for 24 hr, followed by feeding the following day—this is termed alternate day fasting (ADF). For the sake of simplicity, this review will regard intermittent fasting as any dietary protocol that encompasses the lower end of meal frequency (i.e., 1 – 2 meals per day) with prolonged periods of fasting in between. While both methods of dieting—intermittent fasting diet protocol—promote weight loss, neither have ever defied the one ultimate successful weight loss program: “calories in – calories out = weight loss (or gain).”

In other words, both ways of dieting work because they reduce caloric intake relative to expenditure and thereby induce a caloric deficit. If increased or decreased meal frequency were better for weight loss than the traditional 3 – 4 meals per day, then either of the two diets would have to affect one or both factors of weight loss.

To date, there is no evidence to suggest that increasing or decreasing meal frequency, independent of caloric reduction and weight loss, has any effects on energy expended due to structured exercise or non-exercise activity thermogenesis. However, it has been shown that reductions in bodyweight do promote an unconscious reduction in spontaneous activity and therefore a reduction in caloric expenditure. Thus, any diet that reduces bodyweight will likely produce a reduction in energy expended due to structured exercise and non-exercise activity thermogenesis, unless the person consciously compensates by increasing their training volume. Theoretically, if someone increases their meal frequency, it is conceivable that they may increase their non-exercise activity thermogenesis as a factor of preparing more food over the course of the day. Assuming that approximately 50 – 100 kcals are expended due to cooking, this could amount to a couple hundred extra calories burned over the course of 24 hr. However, this is completely speculative and most likely would have negligible effects on the overall caloric deficit from reducing caloric intake and a conscious increase in energy expended due to structured exercise.

Thus, the real question regarding meal frequency is, “which diet protocol most fits with each individual’s lifestyle and dietary preferences?” Nevertheless, whether an individual eats 1 – 3 times per day with prolonged fasts in between, or six or more meals spaced 2 – 3 hr apart, the effects on metabolism and fat loss will essentially be the same. Some aspects to consider when it comes to meal frequency are increased feelings of hunger with fewer meals during a hypocaloric diet and the possible increased feelings of hunger with a shift in feeding pattern from higher frequency to lower. Nevertheless, at the end of the day it comes down to personal preference and the individual’s fitness and performance goals.