Saturday, January 23, 2010

Meal Frequency, Metabolism and Weight Management

You have to eat every few hours or your metabolism will slow down. If you miss a meal, you'll lose muscle. The more often you eat, the faster your metabolism will be. Do any of these statements sound familiar? Are they true? We'll take a look at these questions in brief today.
Eating more often is associated with decreased weight

One reason small, frequent meals are recommended, is in some studies, higher meal frequency has been associated with lower body weights. Oftentimes, those who eat small, frequent meals also eat more nutrient-dense, less calorie-dense foods. In this case, the type of food people select may play a larger role in their reduced body weight, rather than the fact that they ate every few hours. Some cottage cheese with fruit, or a high-protein meal replacement shake, is a much different situation than eating a couple of servings of crackers or a handful of candy. Without considering the type of food consumed every few hours, it would be easy to gain the wrong kind of weight by eating more often than normal.

Another likely reason people who eat more often tend to weigh less is a reduced level of hunger. Because they eat often, they may not get to the point of extreme hunger. It's easy to eat 1500-2000 calories in a single meal of fast food or take-out. If someone doesn't eat all day long, there's a good chance they'll eat whatever sounds the best and is most convenient at the end of the day, which is often a very high-calorie meal.

Eating more often does not raise metabolic rate

Some additional research showed that those who ate more often burned more calories throughout the day. These study results have led to a diet industry that consistently says "eating more often raises your metabolic rate." Again, this is correct to a point, but there are some qualifications involved. Every time you eat, your body burns calories to digest the food you ate. On average, your body burns about 2-3% of the calories you eat from fat, 5-8% from carbohydrates, and 23-28% from protein. This is called the Thermic Effect of Food (TEF) or Diet Induced Thremogenesis (DET). In studies on meal frequency, when the source of calories and the total calories are kept the same, individuals burn the same number of calories over the course of the day.

Let's say an individual eats one meal of 2000 calories, which comes from:

- 55% carbohydrate (275 g)

- 25% fat (56 g)

- 20% protein (100 g)

Obviously, this is a pretty filling meal, and more than most people would eat in a single sitting. In a typical mixed diet, the total effect of TEF is about 10%, meaning in this meal, about 200 calories would be burned in digesting the food. If the same foods were split up equally over five meals, each meal would be 400 calories, which would be:

-55% carbohydrate (55 g)

-25% fat (11 g)

-20% protein (20 g)

It would require about 40 calories to be burned for digestion each meal. For the day, the total calories burned would be exactly the same. Research has shown that as long as the food is exactly the same, it doesn't matter whether it is eaten over the course of one meal or six meals. The effect on metabolism is exactly the same.

Now, let's say that someone is only focused on eating frequently and does not consider where the foods are coming from. They only eat a reasonable amount of protein at dinner. The rest of the meals and snacks during the day are composed of mostly carbohydrate and some fat. Even though they're eating often, because of the foods selected, they actually burn less calories because they come more from carbs and fat. In this case, the increased number of meals could be a disadvantage to weight management. If the calories are the same, but they come from less protein and more fat or carbohydrate, it would have a negative effect on TEF.

In another example, some people who make a point of eating every few hours also make a point of eating a larger amount of protein with each meal. It they eat the same number of calories, but a higher percentage of the total calories come from protein, they will burn more calories in digestion. Basically, any advantage in increasing metabolic rate would come from a higher consumption of dietary protein than from the fact that meals are eaten more frequently. Does that mean there's no reason to eat every few hours. Absolutely not. Eating 20-40 grams of protein every few hours is much easier to eat than trying to eat the same amount in one or two meals. It also allows for more variety in the foods eaten during the day.

Eating every few hours does not prevent "starvation mode"

Another misconception is the idea that the body starts to slow down its metabolism just a few hours after eating. It's possible this idea stemmed from the fact that within a few hours after eating, the body is no longer burning extra calories from digestion. The perception is that the metabolic rate has fallen. In reality, it's back to normal, where it would be without having eaten. It would be possible to raise the metabolic rate again with another meal, but the calories consumed will always exceed the calories burned in digestion, so that would not make sense.

Will your metabolic rate slow down without eating? Yes, but research shows it takes about 72 hours of fasting before metabolic rate begins to slow. In fact, during the first 36 hours of fasting, metabolic rate can increase and then plateau for another 36 hours. Yes, that's correct. Resting metabolic rate tends to stay the same or increase during the first day and a half of a fast. The important point here is that if you're planning to eat something that fits within your nutrient needs for the day, there can be many benefits to eating every few hours. However, if you're not prepared for a meal and feel it's time to eat again, choosing the wrong type of food, like a high-carb, low-protein snack bar, may provide less benefit that eating nothing at all.

In order to control cravings, calorie intake, and ensure enough protein is consumed during the day, eating every few hours is still a good idea. That's why meal replacement powders can work so well for weight management. A 2003 research review in the International Journal of Obesity showed that the regular use of a meal replacement powder led to greater weight loss. It isn't because a meal replacement will increase metabolism by itself. The reason MRPs can work so well for weight management is to control calories and cravings, and increase daily protein intake, which can increase the thremic effect of food and thereby increase total calories burned for the day.


To ensure your diet consists of an appropriate balance of carbohydrate, protein and fat, it's probably best to split up your food intake over several meals. While there is not a metabolic advantage to eating every few hours, there are other reasons to do so. Eating every few hours makes it easier to eat enough protein over the course of the day, which can increase the calories burned over the course of a day compared to a diet of the same number of calories with less protein. Eating ever few hours also helps control cravings, which can actually reduce daily calorie intake. Rather than gorging on an excessively high-calorie meal at the end of the day, many people may eat less total calories by eating smaller meals throughout the day. Aim for at least three whole-food meals, and try to include a couple of smaller meals or snacks. If on occasion you miss a meal though, don't worry. You're not slowing down your metabolism and you're not losing muscle.

In health,

Tom Nikkola


Heilbronn L, Smit S, Martin C, Anton S, Ravussin. Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. Am J Clin Nutr 2005;81:69-73

Heymsfield SB, van Mierlo CAJ, van der Knaap HCM, Heo M, Frier HI. Weight management using a meal replacement strategy: meta and pooling analysis from six studies. International Journal of Obesity (2003) 27, 537-549

Bellisle F, McDevitt R, Prentice A. Meal frequency and energy balance. British Journal of Nutrition (1997), 77 (Suppl. 1), S57-S70

Webber J, MacDonald IA. The cardiovascular, metabolic and hormonal changes accompanying acute starvation in men and women. British Journal of Nutrition (1994), 71, 437-447

McDonald L. Meal Frequency and Energy Balance. Body Recomposition

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