Every day you'll see another post about jumpstarting your metabolism. Maybe it will tell you to eat or avoid certain foods, or maybe just to try a new exercise routine.
One of these guys is famous and they're both sweating (Image: AP)
But few of these articles are backed by solid science. You can't give your metabolism a sudden jumpstart that turns you into a fat-burning, super lean fitness monster. You can, however, live a less crappy lifestyle that causes you to burn more energy more quickly. There aren't quick fixes with immediate results -- that's why they call it "changing your lifestyle".
The word "metabolism" just refers to all of the chemical reactions going on in your body at the same time, including digestion but also turning sugars into energy, building proteins and doing the rest of the chemistry that keeps you alive. Your body combines all these processes to sustain itself and to maintain homeostasis: A constant state of fuel in, energy and waste out, keeping the proper levels of the chemicals you need in check.
Those googling the word "metabolism" are likely interested in losing weight or living a healthier lifestyle, and therefore focusing on the chemical reactions involved in digestion and eating. When it comes those parts of metabolism, homeostasis means "If it takes 1500 calories [6276kJ] to run your body on a given day and do some exercise, your body wants to keep that 1500 level," Jo Zimmerman, Instructor in Kinesiology at the University of Maryland School of Public Health explained to Gizmodo. Sure, the rate at which your body uses fuel to create energy increases while you eat or exercise, but it returns back to normal once you're back at rest.
In other words, your body doesn't want to change its weight. "It's remarkably stable," Zimmerman said.
That means most foods don't cause a meaningful change in your metabolic rate, nor does that rate generally change over time. One exception: Once you're fully grown your body uses less energy, Sarah Kuzmiak-Glancy, assistant professor in Kinesiology from the University of Maryland School of Public Health told Gizmodo. But that decrease in your daily energy requirement doesn't explain the slow weight gain people might associate with getting older. That comes from inactivity.
"People say 'oh, my metabolism slowed down as soon as I hit 30.' No, it didn't slow down a whole lot," said Zimmerman. "Your activity level slowed down. You weren't in college, playing sports after work with your friends," said Zimmerman. "We slow down our physical activity. We're not burning as many calories. That's our creeping weight gain."
So, here you are, out of university hoping to jumpstart your metabolism, trying to avoid packing on the kilos because you've reached your final adult height and don't have time to stay active. Everyone I spoke with said there were two ways to appreciably raise your metabolic rate: Either you can eat food, which causes your body to start using energy, or you can exercise. Caffeine and maybe even capsaicin, the molecule that makes chilli taste spicy, can make your body use up energy a little faster for a short amount of time, said Shawn Arent, Director of The New Jersey Institute for Food, Nutrition and Health Center for Health and Human Performance at Rutgers University. "You're not talking 24 hour regulation," he said. "There's not a huge change in metabolic response -- maybe it's dozens, not hundreds of calories" more energy used. Capsaicin's effects might also come from suppressing the appetite, causing you to eat less, according to a New York Times report.
Ephedrine-based weight loss drugs work similarly to caffeine since ephedrine is a stimulant with a molecular structure a lot like methamphetamine. Ephedrine only offers a handful of kilograms per year worth of lost weight from the added effects of a little faster metabolism, said Arent.
And, just because eating speeds up the rate at which your body does stuff doesn't mean eating breakfast, a major claim of many of those metabolism jumpstart links above, will suddenly turn you into a slim and trim health fiend. "There's nothing magical about breakfast," said Zimmerman. She pointed out that "insidious" homeostasis keeps your metabolism in check throughout the day when you aren't eating, insidious in that your body would rather not lose weight. You should still eat breakfast, but not with weight loss as a goal. It just so happens that eating meals gives you the energy you need to survive.
So, there are no "metabolism jumpstarts". Everyone I spoke to explained that if your goal is losing weight, it's a slow process requiring lifestyle and habit changes -- eating less, eating healthier and exercising more. Assuming you're currently at a state of energy-in-equals-energy-out, Glancy recommended for one pound per week of weight loss (around half a kilo), you would "have to cut your diet down by 500 calories [2092kJ] every day. I always promote 250 calories [1046kJ] of caloric restriction," not eating dessert "and 250 calories [1046kJ] of additional activity". High protein diets seem to positively affect body composition according a few studies by Jose Antonio, assistant professor in exercise and sports science at Nova Southeastern University in Florida, though the companies donating protein powder to those studies are also sponsors to the journals' conference -- so we take the results with a grain of salt. Finally, complete restriction diets don't work for anyone. You must eat.
Cutting some food out of your diet without adding some form of exercise also isn't optimal. While adding muscle won't significantly raise the metabolism, said Arent, "If you're losing weight and lose muscle it has a negative impact on the metabolism," he said. That means strength training like weightlifting is important for maintaining a lower weight. "Losing muscle weight can make it more likely to regain fat later."
Glancy added one caveat, citing a study I reported on previously. "We don't completely know how the gut microbiome, all of the bacteria that live inside of our digestive tract, fits in with all of this," she said. It's possible that our long term eating habits might change the diversity of the bacteria living in our gut, and we might be able to change the way those bacteria aid in our digestion. "It seems like that might be a possibility," she said, "but we're not there yet" in our understanding of how microbiome composition relates to function. Plus, the diet that's best for those bacteria is probably one with more vegetables and fewer refined sugars, the one doctors and nutritionists would recommend anyway.
In short, people make money from selling supplements, they make money from convincing you you're fat and they make money telling you that there are ways to not be fat by buying their product or listening to their advice. But if you're living unhealthily, there aren't jumpstarts or quick fixes to a healthy lifestyle. You have to actually change your habits.