"Eating little and often will increase your metabolism and help you to burn more fat” - true or false?
This is a common statement heard throughout the fitness industry, from PTs through to your new starter or dieter. The theory that more meals per day will increase your metabolism is based on several theories. Most of which, if not all, are not backed by research, or the concepts are flawed. The following is a comparison between the research that has been carried out, and the commonly believed 'facts' in society.
Research, carried out by Cameron et al (2010) (1), states: “We conclude that increasing meal frequency does not promote greater bodyweight loss” (when comparing 3 meals a day to 6 on a weight loss diet). The calories/day in each set of test subjects were equal and, whilst both groups lost weight (due to being in a calorie deficit), there was no significant difference in amount of weight lost in the two groups. As a result, due to the lack of difference, it can be concluded that metabolism was not affected by the change in meal frequency.
This is also seen when people are on a maintenance diet, i.e. eating to keep weight the same. Regardless of whether the meal frequency is higher or lower (1 vs. 3 meals daily), the metabolic rate is not significantly different between the two. (2) Interestingly, the researchers also found “when consuming 1 meal/day, subjects had a significant increase in hunger; a significant modification of body composition, including reductions in fat mass; significant increases in blood pressure and in total, LDL-, and HDL-cholesterol concentrations; and a significant decrease in concentrations of cortisol.”. Given these results, it would suggest that 1 meal per day has positive body composition effects and fat loss, however, this may well be difficult to maintain due to the significant increase in hunger. This would likely lead to excessive eating after a short period of time for many people and, therefore, may not be the most effective option.
Another commonly held, yet incorrect, reasoning for eating more frequently is the belief that, if you eat more meals, the body has to use more energy digesting them and this will increase energy expenditure based on the TEF (thermic effect of food). (3) The examples given in the previous paragraphs show this belief to be incorrect, by finding meal frequency does not alter metabolism. It is important to understand, the amount of energy required to digest food is directly proportional to the number of calories in that meal. The meal composition will also have an effect. For example, meals containing higher protein content will lead to a higher amount of energy used for digestion, compared to one that is high in fat or carbs, as protein is more challenging for the body to break down. Hence, including larger portions of protein can help to improve satiety (feeling full) for longer.
In conclusion, the research above shows that an increased meal frequency does not have a significant impact on metabolism or weight loss. You should choose a meal frequency which enables you to adhere to your diet as a priority. The most important factor for fat loss is to consistently maintain a balanced diet and calorie deficit.
Separately, there is evidence to suggest that increased meal frequency is beneficial for muscle gain, which I will discuss in greater detail at a later date.
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1. https://www.cambridge.org/core/services/aop-cambridge-core/content/view/2CF0DB15A695D6C9F837FB24E16DA3D7/S0007114509992984a.pdf/div-class-title-increased-meal-frequency-does-not-promote-greater-weight-loss-in-subjects-who-were-prescribed-an-8-week-equi-energetic-energy-restricted-diet-div.pdf (Cameron et al (2010))
2. http://ajcn.nutrition.org/content/85/4/981.full (Stote et al (2007))