A 2015 study reveals that consuming omega-3–rich fish oil increases RMR by 14% and increases calories burned during exercise 10%. Other research papers don't indicate a change in RMR, but do suggest a decrease in fat mass when fish or fish oil is consumed often. Some researchers say the anti-inflammatory effects of DHA and EPA contribute to this, though the mechanism is speculation at this point.
Results are mixed; some studies reveal a slight increase in metabolism, while others suggest no change in calories burned but an increase in fat tissue breakdown. While caffeine may have a small role, researchers cite catechins compounds in green tea for any metabolic improvements. Sipping green tea likely isn't going to be a "magic bullet" for weight loss, but it may help you burn a bit more calories.
Research from the University of Utah suggests that people who consume 8 to 12 (8-ounce) glasses of water each day cut more calories than those who only consume 4 glasses. Another study reveals 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 every day.
Eating protein burns a higher percentage of calories, and studies conclude saying that when the same number of calories are eaten, the person eating the higher percentage of protein burns more following the meal, approximately 30 to 60 extra calories per day. But, this increase in energy burned was seen when protein intake increased from 10-15% of calories to about 30%, an amount that's still within recommended guidelines. For someone taking 1500 calories per day, this means swapping about 300 of their carb and fat calories for protein.
The body burns 3 to 4% more calories for the next 2½ to 3 hours after taking in 100mg of caffeine (equal to 1 cup of coffee). This sounds catchy, however when calculated only amounts to 5 to 10 extra calories. Habitual caffeine every few hours during the day increases this total, but often leads to irritability, insomnia, and GI issues from too much caffeine. If you enjoy a daily cup or two of coffee, metabolism will momentarily increase, but not at a level that leads to weight loss.
Capsaicin is the substance in chili peppers that gives them their heat. Many studies reveal 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. But, the increase was only around 10 calories. It certainly doesn't hurt to add spice or chilis to dishes, but those who don't like spicy foods aren't hurting their metabolism by skipping it. There are lots of other ways to burn 10 calories.
A few studies reveals that replacing fats made of long-chain triglycerides (LCTs), like 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 lowered food intake and possible weight loss. Although coconut oil is comprised of similar fatty acids, it is not equal to MCTs and cannot be assumed to have the same benefits.