People have been blaming a faulty metabolism for their extra pounds for as long as there’s been a battle of the bulge. But a “slow” or “faulty” metabolism is an unlikely culprit. Here’s the truth about metabolism and how to get on the right track with losing weight.

Just What Is Metabolism?

It’s a broad term that covers all the work your cells do, primarily pumping ­molecules, such as enzymes, hormones, neurotransmitters and DNA, in or out of cell walls and converting one kind of molecule into another. We measure metabolism as total energy expenditure—the amount of energy needed for all the cells in your body to do that work. The total energy your body burns in a day is the sum of two things—your basal metabolic rate (BMR) plus everything else that you consciously do. Your BMR is the energy used to keep you alive. There’s a general formula to figure out how many daily calories this amounts to…

BMR for women = 5 × weight + 607

BMR for men = 7 × weight + 551

Now here’s the tricky part: Your BMR number could easily fall above or below that total by 200 calories per day, mostly because of your body composition. Tall people burn more than short people…lean people burn more than people who have more fat. But some people just burn more energy than others.

All these variables point to the limitations of online BMR and daily-­expenditure calculators—if the calculation you get is off even by the equivalent of a bag of M&Ms, you could overeat enough to put on a pound every two weeks.

Your metabolism does change over the course of your life span but not at the times people think (or even are taught in medical school)…

Infancy: A baby’s metabolic rate is the highest of any other time in his/her life. A one-year-old burns calories 50% faster for his/her body size than an adult.

Childhood through adolescence: Metabolism slows by about 3% each year, even during the teen growth spurt.

20s through 50s: Total energy expenditure is stable—a “slowing metabolism” can’t be blamed for extra weight, whether you’re a man hitting the big 4-0 or a woman entering menopause.

Age 60 and beyond: Metabolism does start to decline, but at a very gradual 0.7% a year. By age 70, your calorie requirement is down by 7%. In your 90s, you need about 26% fewer calories than you did in midlife.

Blame Your Brain, Not Your Metabolism

When we curse our metabolism for struggles with obesity or fall for the latest metabolism-boosting scam, we are making a fundamental mistake about the way metabolism works. It’s your brain—and specifically your hypothalamus—that’s pulling the strings. Unlike our primate relatives who store excess calories as lean muscle, our bodies are wired to store these calories as fat—it’s our evolutionary burden, designed as a safeguard for a rainy day (e.g., famine). And once you’ve put on that fat, your hypothalamus doesn’t want you to lose it. The brain is very good at getting you to make up for any increase in energy expenditure by increasing hunger.

Research has found that people the world over burn roughly the same number of calories each day, yet the Hadza, the hunter-gatherer people I’ve studied extensively in Tanzania, for instance, are lean while Americans aren’t. To understand why, you need only look at the foods we eat. Take the typical pre-packaged foods at our supermarkets—fiber, protein and anything else that will make you feel full are removed. Sugar, fat, salt and other things to tempt you are added.

Food triggers our reward system in the brain. The variety at our fingertips sabotages our ability to judge our intake because we jump from one set of reward neurons in the brain to another. Example: Ordering dessert even though you’re full from the main course. That savory main course lit up the reward neurons for fat and salt. By the time you’ve finished it, your hypothalamus has successfully extinguished the reward of savory food—you think you couldn’t eat another bite. But dessert is sweet, and those reward neurons are open for business.

What To Do to Lose Weight

You can’t “reset” your metabolism, but you can make diet changes to help thwart your hypothalamus…

Pick any diet. If you look at the research on various diets—low-fat or even one based on eating Twinkies (done just to prove a point)—the bottom line is you have to reduce the overall number of calories you eat. The diet that will work best for you is one that will satisfy you most on the fewest calories. That said, it’s healthier to eat foods that fill you up—vegetables, fruits, meat and fish—and avoid foods that prod you to overconsume, such as sugar, salt and unhealthy fats.

Be suspicious of diets that target one specific nutrient as a weight-loss hero or villain. Any calories that aren’t burned—no matter if they come from starches, sugars, fats or proteins—will wind up as extra tissue (fat) in your body.

Pare down the options at home. If you don’t have potato chips in the house, you can’t eat them.

Set boundaries. Some people do well with hard and fast rules. Example: Decide that you won’t look at the dessert menu when it’s offered…you will shop only the perimeter of the supermarket where healthier options are displayed.

Change your eating habits. People often eat because of food rituals they’ve created. Yours might be to unwind in front of the TV at 9 pm…with a sugary snack. Change the snack, or change the habit.

Weigh yourself every day. This simple act helps you be more conscious about what you’re eating. Also: Studies have shown that people underreport and underestimate how much they eat, so keeping a log can help.

Have a plan to keep the weight off. Weight loss lowers our daily energy requirements, but the hypothalamus-based hunger and satiety systems continue to push you to eat more calories than you burn and put those pounds back on until your weight and daily energy expenditure are back where they were before you lost weight.

Harness the power of exercise. There’s a reason that exercise is called free medicine—it helps to fend off heart disease, diabetes and other consequences of a sedentary lifestyle. A complete absence of physical activity seems to mess up our body’s ability to regulate its metabolic jobs, including the regulation of eating. Basic tasks of cellular hygiene, such as breaking down lipids in the blood or trafficking glucose into cells, start to fall apart.

The only thing that exercise can’t do is move the needle on metabolism in any meaningful way. Getting in those 10,000 steps per day, for instance, burns only about 250 calories—roughly the equivalent of a 20-ounce bottle of soda or half of a Big Mac.

Exercise becomes even more important after weight loss, helping to prevent weight regain.

Keep your guard up indefinitely. As you’ve likely heard before, it takes lifelong change to avoid regaining those lost pounds.

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