The foods you eat trigger the metabolic process and require an expenditure of energy to digest, absorb and transport the food's nutrients to your body's cells. This overall process of stimulation is known as the thermic effect of food, or TEF. Five to 10 percent of your body's daily energy requirements go into processing the foods you eat. Not all foods are created equal, and some foods have a higher thermic effect than others.
Carb vs. Fat vs. Protein
As a general rule, your body expends more energy, or calories, to process proteins than it does to eat and digest carbohydrates and fats. You'll burn up to 30 percent of the calories in lean-protein foods just to process them, putting proteins at the top of the list in terms of thermic effect, according to "The Essential Guide to Healthy Healing Foods." Of the other two macronutrients, carbohydrates require the next highest expenditure of energy to process. Their thermic effect averages between 15 and 20 percent of the calories in those foods. Most easily digested are fats, which have a thermic effect of only 2 to 3 percent. This means that your net caloric gain from fats averages 97 to 98 percent of their total calories, compared with a net caloric gain of about 70 percent of the calories in lean protein.
Registered dietitian Joy Bauer points out that high-quality protein foods offer not only a high thermic effect but also provide a higher degree of satiety, helping to significantly reduce your temptation to snack between meals. Bauer, author of "Joy Bauer's Food Cures," credits this phenomenon to protein's ability to keep blood sugar levels stable, thus avoiding the sharp, temporary ups and downs in blood glucose that are associated with hunger pangs. The key, of course, is picking the best proteins to add to your diet. Ideal foods in this category include milk, rich in calcium that helps to stimulate the metabolic process; egg whites; lean beef and pork; lean chicken and turkey, preferably white meat; salmon and sardines, loaded with heart-healthy omega-3 fatty acids; and tuna. According to an article in the April 28, 2009, issue of the New York Daily News, University of Wisconsin researchers found that adding tuna to your diet helps to reduce your blood levels of the hormone leptin, which is associated with a sluggish metabolism.
To keep your metabolism revved up, personal trainer and nutrition consultant Tom Venuto suggests that you increase consumption of high-fiber carbohydrates. For maximum thermic effect from the carbs in your diet, Venuto, author of "Burn the Fat, Feed the Muscle," recommends oatmeal, yams, sweet potatoes, multigrain cereals, whole-grain bread and pasta, brown rice, broccoli, spinach, salad greens, asparagus, grapefruit, apples, blueberries, pears, cantaloupes and oranges.
Some spices and caffeine tend to prolong and enhance the thermic effect triggered when you consume high-thermic foods, according to master chef Susan Irby, author of the "Boost Your Metabolism Cookbook." Capsaicin, found in chili peppers and paprika, not only bolsters your metabolic rate, but it also decreases cholesterol absorption and increases the enzymes that metabolize fat, Irby says. Caffeine also gives a temporary lift to the metabolic process.