The #1 Worst Food for Your Metabolism, Says Science
Those fortunate few were likely born with a higher basal metabolic rate (BMR) than the rest of us. Your BMR, also known as your resting metabolic rate, is the energy your body requires for your heart to pump blood throughout your body, for breathing, for maintaining tissue like muscle, and for regulating temperature. BMR accounts for about 60 to 70% of your energy expenditure. But there are two other parts to the metabolism picture: your daily physical activity or exercise, called activity thermogenesis, and the thermic effect of food (TEF), that is, the calories used to digest food and turn it into energy.
Research published in 2021 found that our BMR stays relatively consistent from age 20 to 60, and then starts to slow down as we age. So, there's not a lot you can do to change your BMR (although adding muscle through strength training can help because muscle mass burns more calories than fat does).
While our BMR is pretty much a constant, you can temporarily impact your thermic effect of food metabolism depending on the type of food you eat because some foods require more calories to turn into energy than other foods. High-protein foods, for example, have a high thermic effect, meaning it requires your body to work harder to digest them, revving your metabolism. At the same time, there are foods that don't trigger that fat-burning furnace and can actually hurt your metabolism. And those worst foods to eat if you want a higher-revving metabolism are made up of simple sugars without any fiber, such as white bread.
How foods high in simple sugars affect your metabolism
The tool you can use to measure how long a food containing carbohydrate takes to digest and turn into glucose is called the glycemic index. A food that's high on the glycemic index takes less time to digest so it quickly raises the level of glucose in your bloodstream.
These simple carbohydrates—like candy, soda, and sweet desserts—give your body a speedy burst of energy because they are broken down quickly, but then, just as quickly, you will feel lethargic and hungry. They tend to make you ravenous and may spur overeating, so high-GI foods are associated with weight gain. By contrast, complex carbohydrates like whole grains which are low on the GI tend to contribute to weight loss because they take longer to digest and require more calories to do so.
A 2010 study in the journal Food & Nutrition Research illustrated the difference by measuring post-meal energy expenditure during the six hours after subjects ate either meal of processed food (a processed cheese sandwich on white bread) or a "whole food" sandwich made with cheddar cheese on multi-grain bread.
Comparing the measurements from the two meals, researchers found that it took significantly more energy for subjects to digest the whole-food sandwich than the processed food sandwich and concluded that the processed ingredients, especially the white flour, reduced metabolism by 50%. Another study, this one in The American Journal of Clinical Nutrition found that eating a diet with a high-glycemic index promoted overeating, increases in body weight and body fat, and a larger waist circumference in a sample of 191 Danish women.
White bread is particularly bad for your metabolism
"White flour has all of wheat's healthiest parts, like fiber and nutrients, stripped away," says registered dietitian Lisa Moskovitz, RD, CDN, the CEO of NY Nutrition Group. Taking the fiber out makes white bread easy and quick to digest so your metabolism doesn't have to operate at a higher rate and burn more calories to break it down, she says.
So, arguably, the worst foods to eat if you want a higher-revving metabolism are those made up of simple sugars without any fiber. White bread may be the poster child of those foods that slow metabolism, with a glycemic index of about 75, simply because we Americans eat so much of it. Foods are ranked on the GI on a scale of 0 to 100, with pure glucose scoring 100. Some cold cereals rank even higher than white bread at around 81 on the scale. Other high GI, metabolism-slowing foods include granola, white rice, spaghetti, cookies, cakes, pastries, soda, just about anything that's refined and highly processed.
Boosting your resting metabolic rate is difficult to do, but in the short term, you can elevate your fat-burning metabolism by getting more exercise, especially high-intensity effort broken into brief intervals.
An even easier way is by avoiding the worst foods for your metabolism and choosing the best—foods high in protein (lean meats, fish, and Greek yogurt) and fiber like beans and legumes, fruit and vegetables, and whole grains.
Fiber up with these 17 Delicious Recipes Featuring a Simple Can of Beans.