Some people envy others for their fine jewellery or luxury cars, I covet fast metabolisms. I am practically star-struck watching my friend's lean 17-year-old son regularly plow through piles of food, totally carefree (especially because his parents are buying the groceries).
My personal calorie-burning engine is about average, so although I'd like to say I have higher-minded reasons, truthfully what gets me to the gym most days is the reward of being able to eat more. But working out takes time and effort. What if you could burn calories without breaking a sweat, simply by eating certain foods? It's an irresistible idea that gets a lot of media attention.
About 81million search results come up when you Google "metabolism boosting foods," with slide shows, books, blog posts, articles, podcasts and more pointing out what to eat to burn more calories. Predictably, most claims, if not unfounded, are overhyped, over-extrapolated half-truths. I laughed out loud reading some of these pieces - one justified its recommendation to eat sunflower seeds to burn belly fat with a link to a study done on 144 broiler chickens. Seriously, broiler chickens. But, it turns out, some foods and drinks do have solid science behind them as likely metabolism boosters in humans. Even those with the most evidence won't transform you into a calorie-burning machine - but they might make some difference and are worth considering.
One of the tricky things about making sense of these claims is that metabolism is very broadly defined. My Stedman's Medical Dictionary says it is "the sum of the chemical changes occurring in tissue." So, technically, anything that happens in your body is part of your metabolism. But I am zeroing in on a definition of metabolism most of us have in mind when we complain of ours being slow: the number of calories we'd burn in a day if we were just sitting on the sofa. That number is the sum of our basal metabolic rate, the calories the body burns carrying out basic functions such as breathing and repairing cells; and thermogenesis, the calories expended to digest and process food. There is evidence that certain foods and drinks can bump up that total. Physical activity is a third factor contributing to our overall daily calorie burn. It is the most variable factor, and the one we have the most control over.
Green tea is the most celebrated metabolism-boosting consumable, and for good reason. Many studies confirm that the polyphenols called catechins (especially epigallocatechin gallate, or EGCG) and caffeine in green tea increase the calories and fat you burn. A 2011 meta-analysis published in Obesity Reviews found that supplementation with catechins and caffeine mixtures increased energy expenditure by an average of 100 calories a day. But here's the fine print: The amount of EGCG consumed in the studies ranged from 122 and 1,200 milligrams a day, with about 250 milligrams the most commonly administered amount.
According to a report by ConsumerLab.com, the EGCG content of commercially available teas varies widely, from 25 to 86 milligrams per serving. So you'd need to drink about three cups of the highest-quality tea daily to get 250 milligrams of EGCG. That seems doable, and there are other health benefits of drinking green tea, so as long as you keep in mind that it has caffeine, and you don't add sugar to it, there's probably no downside. But if you are considering it as a way to help you lose weight, it might not be the answer you seek. Studies have been mixed as to whether drinking it translates to weight loss - a 2012 report by Cochrane that examined 15 studies showed no significant effect on weight over the long term.
Cayenne pepper is another food that gets a lot of attention as a metabolism stoker, but it is not necessarily the miracle it is often advertised to be. Historically, studies done on cayenne pepper involved consuming up to 10 grams a day, which is the equivalent of 5 1/2 teaspoons. That's a lot of pepper. To put it in perspective, a big part of my job is to develop recipes, and I like spices, but the hottest dish I've ever developed has half a teaspoon of cayenne and serves four people. If you want to do a little experimenting, try putting even a fraction of that 5 1/2 teaspoons on your eggs in the morning. You will quickly see how unrealistic it is. A 2011 Purdue University study looked at more palatable quantities of cayenne and found that even about half a teaspoon in one meal worked to increase energy expenditure, but only by 10 calories, which, incidentally, is the number of calories in one peanut.
Getting plenty of protein and eating whole grains instead of refined can potentially stoke your metabolism. Protein takes the most calories for your body to process, with 20 to 30 per cent of protein calories eaten going to thermogenesis, compared with fat and carbohydrates, which is 0 to 3 per cent and 5 to 10 per cent, respectively. That means that if you eat 100 calories' worth of protein, you are automatically burning 20 to 30 calories of that. We still need a mix of protein, fat and carbohydrate foods to have a healthy metabolism, so don't be that person ordering a plate of three chicken breasts for lunch, as I saw a guy do at my gym's cafe. (It was all I could do not to say something!)
But although the Dietary Reference Intake is 46 grams a day for women and 56 grams for men, there may be a metabolic benefit to aiming for 70 to 90 grams of protein a day, not only to harness the thermogenic effect but also because it could help in the maintenance of muscle, the central driver of your basal metabolism. (A four-ounce chicken breast has about 34 grams of protein.) When it comes to carbs, burning more calories is yet another incentive to choose whole grains over refined. A 2017 study in the American Journal of Clinical Nutrition found that people given whole grains burned 92 more calories a day than those given refined grains.
So drink green tea, enjoy as much cayenne on your food as you can tolerate, get enough protein and go for whole grains. It might just help a smidge. But, overall, don't lean on individual foods for a big metabolism boost. Your best bet for burning calories is to get moving.