The truth about metabolism: what really affects your metabolic rate
The truth about metabolism: is a slow metabolism to blame for excess weight? Do spicy foods speed up your metabolism? Can you change your metabolic rate, and if so, how?
Many people, particularly women, are quick to blame a slow metabolism for their extra kilos. But you should not jump to conclusions. The idea that a slow metabolism is always responsible for excess weight is one of many misconceptions about metabolism, says James Hill, Ph.D., director of the University of Colorado Health Sciences. Even if your metabolism is slower than average, it does not necessarily mean you are destined to be overweight.
With so much confusion surrounding metabolism, we asked experts to explain the myths and misconceptions. From chili pepper capsules to physical exercise, we explore whether and how you can influence your metabolism to shed those extra kilos for good.
Q: We hear about metabolism all the time. What exactly is it?
A: In the simplest terms, metabolism refers to the rate at which your body breaks food down into nutrients, says Hill. Someone with a fast metabolism can absorb and use calories from food more quickly, which in some cases does help prevent excess weight gain.
Q: What factors affect metabolism?
A: Body composition is the main factor determining your resting or basal metabolic rate: the number of calories your body needs to sustain itself at rest. According to Hill, the more fat-free mass you have (muscle mass, bones, internal organs, etc.), the higher your basal metabolic rate. This also explains why the average man’s metabolism is 10 – 20 percent faster than the average woman’s. Similarly, a larger woman (whose body weight, and therefore probably both fat-free mass and fat mass, are considerably greater) may have a basal metabolic rate up to 50 percent higher than a slim, lean woman. Heredity and hormones, such as insulin and thyroid hormones, are important factors that determine metabolic rate, although stress, physical activity and any medication you take also play a substantial role.
Q: So are we born with either a fast or a slow metabolism?
A: Yes. Studies of identical twins confirm that your metabolic type is largely determined at birth. Even if you have a naturally slow metabolism, being overweight is not necessarily inevitable. Losing fat may be considerably harder, but it is still almost always possible, says weight-loss expert Pamela Peeke (M.D., M.P.H., professor of medicine at the University of Maryland). You may never burn calories as quickly as, say, Serena Williams, but you can certainly increase your basal metabolic rate to some extent by moving more, training and increasing the proportion of muscle mass in your body.
Q: I remember being able to eat whatever I wanted when I was younger. Now, as the years go by, my metabolism seems to have slowed down. What is happening?
A: If you can no longer eat as freely as you used to without gaining weight, insufficient physical activity is very likely the main culprit. From the age of 30, the average woman’s basal metabolic rate drops by 2 – 3 percent every ten years, mainly because of declining physical activity and a reduction in the proportion of muscle mass in the body, says Hill. Fortunately, a considerable amount of that lost muscle mass can be regained through regular physical training.
Q: Is it true that extreme diets and swinging from one extreme approach to another seriously damage our metabolism?
A: There is no conclusive scientific evidence that drastic fluctuations in calorie intake permanently damage your metabolism, Hill notes. What certainly does happen, however, is that when you substantially reduce your calorie intake to lose weight, your basal metabolic rate drops fairly quickly by 5 – 10 percent.
Q: What types of training are best for increasing your metabolic rate?
A: Experts agree that strength training is the most effective way to build muscle and maintain muscle mass. However, the view that additional muscle mass alone has a negligible effect on metabolism is also fairly widespread. Every 1 (kg) kilogram of muscle adds 33 kilocalories to your basal energy expenditure, says Gary Foster, Ph.D., a professor at the University of Pennsylvania.
When it comes to physical activity, high-intensity endurance training (as measured by heart rate) burns the most calories and therefore gives your metabolic rate the greatest boost (translator’s note: this clearly means activities that engage many muscles at once and keep your heart rate high, such as circuit training). Of course, this boost is temporary, and workouts certainly have no direct, lasting effect on your basal metabolic rate. Depending on the intensity, a solid endurance workout can increase your metabolic rate by 20 – 30 percent. After the workout, your metabolism remains elevated for a few hours before gradually returning to its previous level.
Q: Do the nutrients we consume affect our metabolism, and if so, how?
A: Most scientific research suggests that food choices have no significant effect on basal metabolic rate. In other words, fats, proteins and carbohydrates affect metabolism and its rate in relatively similar ways. “The slight increase in metabolism from protein may be somewhat greater than that from fats or carbohydrates, but the difference is still negligible,” says Foster. What matters is how much you eat. If you eat less than you burn each day, your metabolic rate automatically starts to decline. When food is restricted, your body conserves energy to keep its vital functions operating normally. The more you restrict calories, the more your metabolic rate drops.
For example, on a very low-calorie diet (800 Kcal or less), your metabolic rate can easily drop by 10 percent or more, says Foster. Metabolism begins to slow within 48 hours of receiving insufficient energy to meet your expenditure. To avoid slowing your metabolism, it makes sense to take a sensible approach to any diet and avoid expecting miraculous results in a miraculously short time. The average woman should never let her calorie intake drop below 1200 Kcal a day, Foster notes.
To lose 450 g of fat a week, you need a deficit of 500 Kcal a day. The best way to achieve this deficit without slowing your metabolism is to combine training and diet sensibly, rather than relying solely on calorie restriction. For example, reduce your daily food intake by – 250 Kcal and add enough physical activity to burn an extra 250 Kcal…and you have your daily deficit of – 500 Kcal.
Q: Do spicy foods such as chili peppers and curry boost metabolism?
A: Yes, but unfortunately, the effect is too small to produce any weight loss. “Anything that raises your body temperature temporarily increases your metabolic rate to some extent,” says Peeke. However, the rise in body temperature caused by spices is so small and short-lived that it makes virtually no difference on the scales.
Q: What happens to my metabolism when I lose weight?
A: As you lose weight, your basal metabolic rate also slows because there is less body weight to supply with energy. Your body therefore needs less energy than before to sustain its vital functions. In other words, you no longer need as much fuel to feel full or to train, because your body is smaller. If you do not adjust your diet as you go, you will soon reach a plateau and stop losing weight. To break through that plateau and continue losing weight through fat loss, if that is your goal, you need to keep reducing calories gradually, without making overly drastic cuts, or increase the frequency or intensity of your workouts.
Q: What about supplements that promise “miracles” and claim to set our body fat “on fire”?
A: Do not believe them! No tablet, capsule or sachet will miraculously increase your metabolic rate enough to make a noticeable difference to weight loss, says Peeke. If you want to speed up your metabolism to lose weight, the best option is simply to be physically active and burn energy.
Q: Can any medications slow metabolism?
A: Some medications do slow metabolism, including those used to treat depression and bipolar disorder. If you take medication that causes weight gain, it is advisable to speak to your doctor about possible alternatives.
Ultimately, metabolism depends on a wide range of factors. That is why two women (or men) of the same age, height and even weight can have completely different basal metabolic rates. These various factors also explain why some people can eat whatever they like without becoming overweight, while others seem to gain extra kilos just by reading the dessert menu. Knowing your metabolic rate certainly helps you put together a training program and nutrition plan suited to your metabolic type, says Pamela Peeke, author of “Fight Fat After Forty”.
The truth about metabolism: will a slow metabolism make you fat? Can spicy foods spike it? Could a pill speed it up?
Author: Janar Rückenberg (translation)Source: Turg.Fitness.ee
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