Is my metabolism affected by what, how, and when I eat?

Kernels of Truth

Since the beginning of time, people have expanded the powers of food beyond simply meeting nutritional and energy needs. The belief that specific foods can cure health problems is a longstanding cultural tradition: eating chicken soup to cure a cold and oysters to enhance fertility are just two examples.We really want to believe in the power of foods. It is not surprising that specific foods and eating regimens have made their way into the folklore of weight loss.With great optimism, people embrace the latest new food or way of eating with the hope that it will put them on the path to sustained weight loss.

The magic of a single solution for weight loss focuses on just one aspect of a food, supplement, or activity.This is similar to the tale about the three blind men and the elephant: Three blind men are asked to describe an elephant. One of them touches the trunk, another touches the tail, and the third touches the foot. Each of the blind men accurately describes what he touched, but none of them can describe the elephant because the animal is bigger than a single body part.

Weight-loss myths are similar in that they isolate a particular feature that may be true and offer it as a solution to the entire problem of weight loss. It is possible to find at least one study to prove that each of the weight-loss boosters below does lead to superior weight loss. Often the one study that is publicized on television or read about in a magazine is the only study that shows results, but it is easy to believe the story because the study results are true, even if only just once.

But rigorous science requires a study to be replicated by other scientists and for them to observe the same results. Few of us have the inclination to track down all the research studies on a topic in order to find out if there is general agreement about the pool of scientific evidence on a specific weight-loss booster.We have done so for you. When the scientific community makes its judgment on a particular issue, it is based on all of the evidence, not just on one or a few isolated studies.

Building more muscle mass does increase metabolism. Because muscle is the engine that drives the body, it burns more calories than fat, so activities that speed up metabolism can boost calorie burning and weight loss.

Is it possible to lose weight on diets that promise to speed up metabolism? Probably not. If you do lose weight, it is not due to a faster metabolism. Read on to discover that the secret to weight loss is calories and that the weight loss achieved through a metabolism boosting diet is also due to calories.

The Whole Truth

It’s All about Calories

Body weight reflects the balance between calories in and calories out. The food we eat supplies calories. Our body burns calories three ways: through resting metabolism, the calories burned as the body keeps itself running 24/7; during physical activity; and in digesting and absorbing food. A steady body weight means a balance between food and calorie burning. Gaining or losing weight is the sign of an imbalance.

Calories and Weight
Calories in greater than calories out = Weight gain
Calories in equal to calories out  = Steady weight
Calories in less than calories out  = Weight loss

The only scientifically proven method for losing weight involves the creation of a caloric imbalance. At the end of the day, the only true way to lose weight is to eat fewer calories in food and/or burn more calories. This has been shown time and time again in decades of rigorous scientific studies. One example of the hundreds that exist was done in Switzerland. Fifty-four obese people had their calories restricted to 1,100 per day. Different combinations of foods and meal timing were tested.There was no difference in weight losses; only the calories made a difference.

A Faster Metabolism Burns More

It takes a shortfall of about 500 calories a day to lose 1 pound per week and 1,000 calories a day to lose 2 pounds weekly. The most effective method to create this shortfall is to cut calories from food and also to boost metabolism. But despite the promises of so many popular diets and products, metabolism can be boosted in only a couple of ways: exercising more and speeding up heart rate.

One of the chief benefits of exercise is that it revs up metabolism. The reason is simple. Individuals who exercise on a consistent basis maintain high levels of lean muscle tissue throughout their lifetime. They also build new muscle. Lean muscle tissue sustains high levels of metabolism. In fact, lean muscle tissue burns seventy times as many calories as fat does. Exercise burns calories, and longer periods of exercise mean greater calorie burning.

While it is true that an increase in lean muscle mass increases metabolism because muscles burn a lot of calories, weight loss almost always results in some loss of muscle mass. The muscles have less weight to carry around, so less muscle is needed. People who follow extreme diets to get a fast weight loss can significantly reduce their lean muscle tissue and thereby slow their metabolism.

A popular theory widely reported in the media is that exercise increases metabolism during activity and for a period of time after the activity is completed. Unfortunately, studies that have researched this concept do not have consistent results. In general, studies on humans suggest that metabolism increases when the amount of body muscle increases but that the number of extra calories burned after exercise is relatively small. And no studies have directly linked the aftereffects of exercise with significant weight loss. It’s the calories expended doing the exercise that boost weight loss, not the aftereffects of exercise on metabolism.

The second way to increase metabolism is to increase heart rate. The heart and other organs contribute to the resting metabolic rate—the calories the body burns just to keep itself going. In a controlled study that looked at the effects of amphetamines on weight loss, the stimulants caused greater weight loss. Heart rate and blood pressure went up and food intake went down, a side effect of feeling hyper and too nervous to eat. Many weight-loss supplements contain chemical or herbal stimulants, including caffeine, guarana, and the now-banned ephedra, which speed up metabolism by pumping up the heart rate. Most of the supplements and over-the-counter products that are marketed to promote weight loss contain stimulants, albeit at a lesser strength than that found in prescription amphetamines. Like their more potent cousin, these compounds are marketed as “fat-burning” and cause weight loss by increasing your heart rate and blood pressure and decreasing your appetite.

These stimulants can work, but they do so at a cost to the body. Negative side effects include insomnia, nervousness, anxiety, and in extreme cases, death. Increasingly, some of these products (including the ones that were most effective, like phenylpropanolamine and ephedra) have been banned because of the negative side effects.

A careful look at the ingredient list of many herbal remedies reveals the truth—herbal diuretics that cause the body to lose fluid through urination and herbal laxatives. Just because the package says the product is natural or herbal does not mean it is healthy. A combination of stimulants, diuretics, and laxatives does not add up to a safe and sensible way to lose weight.

Over the years, other foods and products have been falsely promoted as metabolism boosters for weight loss. Grapefruit, for example, was said to have compounds that speed up metabolism; an added promise was that eating and digesting grapefruit actually uses up more calories than are in the grapefruit. Celery is often promoted as a food that burns more calories than it supplies. But there is no scientific proof that calories spent digesting and absorbing can be pumped up by eating particular foods.

The Source of Calories Does Not Affect Your Weight Loss

Which is best for weight loss—a diet low in carbohydrates and high in protein, or a diet balanced in carbohydrates, protein, and fat? That’s been a question that has received a lot of scientific attention, and science is showing a firm conclusion—it does not matter. According to dozens of research studies, no particular type of diet speeds up metabolism more than another. In 2004, a complete review of all research studies on the topic concluded that following a low-carbohydrate and/or high-protein diet did not affect the rate of metabolism. Diets with differing proportions of macronutrients work because they reduce calories, albeit in disguise.They have no special effects on metabolism.

Eat More, Lose Weight?

Diets that promise more food for greater weight loss are usually variations on very low-fat diets. Because they focus on naturally low-fat, low-calorie foods like fruits and vegetables, they supply a greater volume of food for fewer calories.The foods are also ones that are thought of as harder to digest, suggesting that they burn more calories during digestion. However, as with other types of diets, very low-fat diets work because they are lower in calories. They do not speed up metabolism and do not require digestion to go into overdrive.

No Food or Food Combination Burns Body Fat

The term thermogenesis, or calorie burning, became very popular in the mid-1990s when a popular weight-loss book suggested that certain foods caused the body to burn extra energy in order to digest and absorb them. The concept of thermogenesis is based on science, but the relative contribution of this extra energy burning is so minor that it
is irrelevant for weight loss.

“Fat-burning” foods do not burn fat. Highly acidic foods like grapefruit, lemon juice, and vinegar are said to melt away fat because they are so acidic. This explanation sounds logical but does not work in real life. Certain food combinations are said to create chemical reactions in the body that promote loss of body fat.This promise cannot be proven, and these foods do not boost metabolism.

Some foods like caffeine-containing beverages and capsaicin containing chile peppers have been linked with a boost in calorie burning. Caffeine is a mild stimulant, and high dosages of caffeine raise the heart rate. Chile peppers cause the body to sweat and to feel stimulated. In one study, capsaicin did cause increased fat burning in a group of people who had lost weight, but it did not help them maintain their weight loss. Results were similar for green tea, a beverage that contains caffeine and other components reported to boost metabolism. When put into rigorous studies, neither demonstrated a significant effect on weight loss.

Eating Patterns Do Not Make a Difference

Eating three times daily or six times daily? Having a small breakfast and big dinner or big breakfast and small dinner? Which is best for burning calories? Again, it does not matter. As long as calories remain the same, meal sizes relative to each other do not affect weight loss. A series of well-controlled experiments that looked at the effect of meal timing on metabolism was conducted in a clinical research center at a university. Regardless of the meal timing—eating once a day or several times a day, eating at night or in the morning—weight loss stayed the same when study subjects ate the same number of calories. The researchers concluded that the body’s regulatory systems are extremely fine-tuned.

So if meal timing does not change metabolism, how does meal timing work? It promotes weight loss by throwing off normal eating routines in a way that leads to eating fewer calories. Say that you are told to eat only fruit before noon. If you are a breakfast eater, then not being able to eat cereal, toast, a sausage biscuit, or your usual breakfast foods automatically cuts calories. There is nothing metabolically magical about eating only fruit in the morning. The same is true if you tend to snack in the evening and go on a “metabolism-boosting” diet that prohibits eating after 7:00 P.M.

That said, meal timing is important because eating plans have to be livable and adaptable to our different lifestyles.Work schedule, family structure, exercise routine, and numerous other factors help determine the best eating schedule. Say a person works the night shift and sleeps during the day. She may want to eat dinner with her family even though that meal is really breakfast for her, then eat lunch in the middle of her work shift and a small breakfast with her family before going to sleep. A person who works full-time and exercises daily after work may want to eat breakfast, lunch, then two mini-meals, one midafternoon before exercise and one at night after exercise. No one schedule is better than another.

You may have heard how important it is to eat breakfast. It is true that numerous studies have shown that people who eat breakfast are much less likely to gain weight than those who do not eat breakfast. Eating breakfast provides essential nutrients, sets the body up with energy for the day, and is linked with less eating later in the day. The effect is not on metabolism; it is on lifestyle and habits.

Some weight-loss proponents recommend eating a bigger breakfast, followed by a smaller lunch and an even smaller dinner. The theory is that the majority of calories are eaten toward the beginning of the day when the body needs them most. This approach works in theory but has not undergone the rigorous studies needed to prove or disprove its impact on sustained weight loss. It is also not practical for most people.

Restrictive Diets Reduce Calories

As with diets that throw off eating routines by changing meal timing, a diet that imposes almost any type of restriction will reduce calories by forcing a change in habits. Whether it’s avoiding gluten and dairy, not eating a protein food and a starch within four hours of each other, consuming bowls of cabbage soup, or only eating fruit before noon, following rules that restrict the type of food eaten, the time of day food is eaten, or how frequently a food or food type is eaten will reduce caloric intake.

Let’s look more closely at the concept of separating different types of foods. Say that a diet is based on avoiding eating starches and protein foods together in a meal, a basic premise of a popular diet in the 1990s. That means no cereal (starch) and milk (protein) or toast (starch) and egg (protein) at breakfast, no sandwich at lunch because starchy bread typically is combined with a protein food, and no potato, rice, pasta, or bread (all starches) with meat, chicken, or fish (all proteins) at dinner. Imagine how much less you would eat if you were told to avoid traditional food combinations!

What about eating three standard-size meals and no snacks versus eating six or even eight mini-meals? The end result depends on the routine that is being changed and the total amount of food eaten. A frequent snacker might eat less food on a three-meal no-snack diet and lose weight. The mini-meal eater could lose weight as long as the calories in the mini-meals added up to less than he or she was eating before. The science in this area is inconsistent. Some research says that eating fewer, bigger meals allows the body to burn a few more calories digesting and absorbing foods. But there is no strong research showing that meal frequency and size affects weight loss as long as calories are the same.

The Placebo Effect Works

For every one of the myths and gimmicks about foods, supplements, and food timing and combining discussed in this article, there are a dozen more being promoted. These myths are so prevalent because each has a kernel of truth—a small part of the myth based on science. It is the fantastic story that gets wrapped up with the truth that creates a myth rather than a valid, long-lasting way to lose weight.

The placebo effect happens when a person believes that there is a direct cause-and-effect relationship between two things even if it does not exist. Because the person believes in the relationship, however, his or her behavior changes in a way that produces the anticipated effect.

Rigorous scientific studies include a placebo group and a group that is actually getting the treatment. This is the only valid way to ensure that it is the treatment and not the placebo that is producing the effect. Many promising treatments in the area of weight loss lose their luster when they are evaluated in a rigorous scientific study that includes a placebo group. For example, acupuncture is often touted as a weightloss treatment. When tested against a placebo, however, it has been shown to be ineffective.The same has been shown for subliminal tapes to induce weight loss.

It’s about Behavior Change, Not Metabolism

Ultimately, behavior changes that support eating fewer calories and being more active lead to weight loss. Despite this reality, only one-third of Americans trying to lose weight use the strategy that is the fundamental foundation of weight loss. Sustainable weight loss does not result from a revved-up metabolism or the unique properties of specific foods. However, particular eating behaviors and patterns, such as meal frequency, meal timing, or following a specific dietary pattern, and nutritional factors, like the energy density of food and the amount of fiber, may affect caloric intake and thus weight loss.

Here is an example of a suggested behavior change that works, even though the premise for the change has nothing to do with a metabolism. Many programs will tell you that you should not eat after 7:00 P.M. because “food eaten in the evening turns to fat.” The truth is that any food turns to fat if calories in are greater than calories out. The time of day that it is eaten does not matter. However, many people consume a large portion of their daily calories in the evening. Television viewing, an evening activity for many, is also associated with increased caloric intake and “mindless” snacking. A dietary regimen that restricts evening eating works because it limits calories. That, in turn, helps burn fat.

The Bottom Line

The famous baby doctor Benjamin Spock was known for telling young mothers,“Trust yourself, you know more than you think you do.” The same holds true for weight loss. There is no reason to feel bad if you have tried the diets and products that promise a metabolism-inspired weight loss. Everybody wants to believe in the promise, and the pseudoscience that goes along with many of the claims seems to make a lot of sense. But when it comes to achieving weight loss that lasts, a combination of instinct and a complete disclosure of the pool of scientific studies is the way to figure out what is real and what is a myth.

It is much more important to find an eating style and exercise routine that suits your life and that you can stay with over time than trying to follow an uncomfortable or overly restricted regimen in the hopes of boosting your metabolism. Ultimately, it is livable changes to your lifestyle that will make the big difference and help you lose the weight and keep it off.

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