Just as cars run on petrol, our bodies rely on kilojoules for everything we do-from breathing and thinking to watching This Is Us with a giant tub of popcorn.
Metabolism is the process of turning the kilojoules we eat into energy. How many you need simply to exist (and hence how much butter you can put on that popcorn without gaining weight) is called your basal metabolic rate, or BMR, and it’s different for everyone.
But can we make our BMR work faster? From food fads to fanatical workouts, take this quiz to find out if everything you think you know about your metabolism is true.
True or false: You’re stuck with the metabolism you inherited.
The answer: False
“Metabolism is hereditary—but we can influence it” through lifestyle choices, says Endocronologist Dr Robert Kushner. Building muscle through weight training (two sessions a week is ideal) is key to boosting BMR, because lean muscle mass burns about 60 to 80 kilojoules per kilo. Aerobic exercise is also important: Aim for 30 minutes, five times a week. “Try anything that raises your heart rate, like hiking, running or biking,” Dr Kushner says, but mix it up. “When the body adjusts to a certain level of intensity, less energy is required to perform the same task,” he says. “But increasing the variety of exercises, to engage more muscles, adds to your kilojoule burn.”
True or false: Your metabolism slows down with age.
The answer: Not if you don’t let it
Maintaining muscle mass in your 20s and 30s will help, because starting at age 40, testosterone levels begin to drop, and the hormone is important to muscle growth, says women's health expert Dr Pamela Peeke. The key, again, is exercise. Experts are learning that along with strength training, high-intensity interval training (HIIT), which alternates intense movement with a more moderate pace, has the greatest impact on metabolism. If you hike, take the hillier route. A runner? Add in sprints. “Just 20 to 30 minutes of HIIT, two or three times a week, is enough to see results,” Dr Peeke says.
True or false: Your diet can’t significantly raise your metabolism.
The answer: True—as far as we know!
“Research on consuming foods for a faster metabolism is lacking,” says researcher Dr Kelly Pritchett. While foods like chilli peppers (which contain heat-generating capsaicin), caffeine, and apple cider vinegar may increase metabolism, the effect “is slight and temporary,” Pritchett says, and the downsides—unpleasant taste, upset stomach, or the coffee jitters—aren’t worth it. What about so-called “negative kilojoules” foods? While eats that are high in protein and fibre do require more energy to digest, adds Pritchett, “the metabolic increase is likely negligible.”
True or false: The timing of when you eat matters when it comes to your metabolism.
The answer: Sorry, but it’s true!
“Eating carbs in the evening leads to metabolic problems, because the body is more resistant to insulin at night,” often resulting in higher blood sugar, says clinical investigator Dr Aaron Cypess. Over time, higher blood sugar, even in nondiabetic people, can contribute to weight gain and complications such as heart disease. Protein-rich foods are not great, either. “While high-carb foods will more directly raise blood glucose and be converted to fat,” Dr Cypess says, “it takes only a few steps for the liver to convert protein to carbs and fat.” Bottom line: Too many kilojoules, no matter the source, will be stored as fat, so eat light at night.
True or false: Intermittent fasting increases metabolism.
The answer: False
There’s no evidence to suggest that intermittent fasting, a trendy approach to eating that severely limits calories either on certain days or for certain periods of time, ups metabolism, says bariatric dietitian Melissa Majumdar. One study measured the resting metabolic rate of non-obese men and women who fasted every other day for three weeks, and found no significant increase. Also, hunger didn’t decrease on fasting days, which indicates that such a diet might not be sustainable.
“If you deprive yourself of certain foods, you may overdo it in the long run,” Pritchett says. “I think the same could happen with intermittent fasting-you may be so hungry that you choose the wrong foods.” While some do lose weight, that’s because they eat fewer calories, not because their metabolism speeds up.