The Claim: Eating cold-water fish (like salmon, mackerel, and tuna) increases RMR and fat loss thanks to two omega-3 fatty acids (DHA and EPA) that play a role in regulating metabolism.
Metabolism Effect: A 2015 study suggests that consuming omega-3–rich fish oil increases RMR by 14% and increases calories burned during exercise 10%. Other studies don't indicate a change in RMR, but do suggest a decrease in fat mass when fish or fish oil is consumed regularly. Some researchers suggest the anti-inflammatory effects of DHA and EPA contribute to this, though the mechanism is speculation at this point.
Our Verdict: You likely won't see a big boost from adding fish to your diet, unless it's in combination with smart food choices and activity. However, eating fish like salmon twice a week is already encouraged by the American Heart Association to reduce heart disease risk, so if it also helps metabolism, why not?
The Claim: Drinking plenty of water speeds up metabolism, and the colder water, the greater the boost.
Metabolism Effect: Adequate hydration makes a difference. Research from the University of Utah suggests that individuals who consume 8 to 12 (8-ounce) glasses of water each day burn more calories than those who only consume 4 glasses. Another study suggests an extra four to seven calories were burned for every cup of cold water consumed, much of which was due to the extra energy used to warm the water. If you drink 8 (8-ounce) glasses or more of cold water, this adds up to around 56 extra calories burned daily.
Our Verdict: Stay hydrated by drinking at least 64 ounces daily to maintain the body’s metabolic processes, as well as possibly burn extra calories. Can’t tolerate cold? Room-temp water still provides some effect.
The Claim: Protein requires burning more calories during digestion than carbohydrate and fat, so eating a high-protein diet increases metabolism and makes weight maintenance easier.
Metabolism Effect: It's clear that eating protein burns a higher percentage of calories, and studies suggest that when the same number of calories are eaten, the individual eating the higher percentage of protein burns more following the meal, approximately 30 to 60 extra calories per day. However, this increase in energy burned was seen when protein intake increased from 10-15% of calories to approximately 30%, an amount that's still within recommended guidelines. For someone consuming 1500 calories per day, this means swapping about 300 of their carb and fat calories for protein.
Our Verdict: Don't go low-carb, but look for ways to incorporate some protein at each meal and snack. Protein can come from animals or plants such as legumes, soy, and nuts. Another benefit of adding protein is that it increases satiety, which can go along way controlling appetite and hunger.
The Claim: Because caffeine is a stimulant, it causes a short-term increase in RMR, so regular caffeine intake boosts metabolism.
Metabolism Effect: The body burns 3 to 4% more calories for the next 2½ to 3 hours after taking in 100mg of caffeine (equivalent to 1 cup of coffee). This sounds good, but when calculated only amounts to 5 to 10 extra calories. Regular caffeine every few hours during the day increases this total, but often leads to irritability, insomnia, and GI issues from too much caffeine.
Our Verdict: If you enjoy a daily cup or two of coffee, metabolism will temporarily increase, but not at a level that leads to weight loss. Keep caffeine intake to 400mg or less to avoid side effects, and don't negate caffeine's small metabolism boost with more calories from cream and added sugars.
The Claim: Eating spicy foods increases the calories burned by triggering an increase in body temperature.
Metabolism Effect: Capsaicin is the compound in chile peppers that gives them their heat. Numerous studies suggest that capsaicin raises metabolism, and a 2011 study found that taking in 1g of cayenne pepper (between 1⁄4 to 1⁄8 teaspoon) increased the calories burned following the meal. However, the increase was only around 10 calories.
Our Verdict: It definitely doesn't hurt to add spice or chiles to dishes, but those who don't like spicy foods aren't hurting their metabolism by skipping it. There are plenty of other ways to burn 10 calories.
The Claim: Along with reducing heart disease, dementia and cancer risk, green tea also speeds up metabolism.
Metabolism Effect: Results are mixed; some studies suggest a slight increase in metabolism, while others suggest no change in calories burned but an increase in fat tissue breakdown. While caffeine may play a small role, researchers cite catechin compounds in green tea for any metabolic improvements.
Our Verdict: Sipping green tea likely isn't going to be a "magic bullet" for weight loss, but it may help you burn a few more calories. And, even if it doesn't, you're still saving calories by swapping it for a soda and possibly reducing risk for other conditions.
*Speculated but not proven
The Claim: Swapping vegetable oils for coconut oil boosts metabolism thanks to more efficient breakdown in the body.
Metabolism Effect: A few studies suggest that replacing fats made of long-chain triglycerides (LCTs), such as olive oil, with medium-chain triglycerides MCTs) increases the calories burned by 13 to 72 calories daily. There are also reports of greater satiety when LCTs are replaced with MCTs in the diet, suggesting reduced food intake and potential weight loss. Although coconut oil is composed of similar fatty acids, it is not equivalent to MCTs and cannot be assumed to have the same benefits.
Our Verdict: We'd be remiss to discount the possible effect of MCTs on metabolism, but more research is needed to determine the specific effects of coconut oil. In the meantime, coconut oil should be treated like all other oils and used in moderation.
*Speculated but not proven