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3 Primary Sources of Calories in a Diet

author image Amber Smith
Amber Smith is health and fitness editor at "The Syracuse Post-Standard," where she has worked since 1988, specializing in medicine, health and fitness. She has also written for "Woman's Day," "Parenting," "Weight Watchers Magazine," and She blogs about dementia at
3 Primary Sources of Calories in a Diet
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The calories we consume provide energy and nutrients that our bodies require. Our best health comes from making good food choices from among carbohydrates, proteins and fats--and sometimes that is tricky. High-fat foods are also high in calories, but many low-fat or nonfat foods can also be high in calories. Some protein sources are also good sources of carbohydrates; some contain high levels of fats. Counting calories may help you lose weight, but focusing on the three sources of calories can bring better overall nutrition.

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Whole-grain bread is a good source of carbohydrates.
Whole-grain bread is a good source of carbohydrates.

Carbohydrates come from grains, bread and pasta, fruits, vegetables, legumes and dairy products. They're either classified as simple or complex, depending on their molecular structure.

Of the calories we consume in a day, U.S. Department of Agriculture dietary guidelines say about 55 percent should come from carbohydrates, which provide about 4 calories per gram. As they are digested, carbohydrates are broken into simple sugars, called glucose, which the body uses in multiple ways, including to keep the brain functioning and to build cartilage, bone and nervous system tissues.

Not all carbohydrates are equal, however. By eating whole grains and products made from unrefined grains, you can derive benefit from fiber and nutrients that are removed during the refining process. Some good choices include brown rice, angel food cake, oatmeal cookies, sweet potatoes, lentils, raisin bran, couscous and barley.


Nuts can be a good source of protein.
Nuts can be a good source of protein.

About 15 percent of our calories each day should come from protein sources, which--like carbohydrates--provide about 4 calories per gram, say USDA dietary guidelines.

Because men generally have more muscle mass, they require more protein than women. Typically, women require 46 g of protein per day; men require 56 g, according to dietitian Lisa Hark, Ph.D., R.D., and Darwin Deen, M.D., in their book, "Nutrition for Life." Physical activity level and your body's need for nitrogen and essential amino acids can increase your protein requirements, as can pregnancy, growth during childhood or recovery from surgery.

Meat is a primary source of protein in America, but plant sources are also available, including legumes, nuts, seeds and grains. Plant sources, other than soy, must be combined with other foods since they do not provide the full complement of amino acids that our bodies require for normal functioning.


Salmon is one fish choice containing healthy fats.
Salmon is one fish choice containing healthy fats.

Fats are an essential part of our diets as well. Our bodies use fats to form the major part of all cell membranes, and fats play a vital role in the absorption of certain vitamins. USDA dietary guidelines say up to 30 percent of our calories should come from fats, which provide about 9 calories per gram.

The best choices are unsaturated fats (which include plaint oils, avocados, peanuts and pecans) and polyunsaturated fats (which include salmon, tuna, lobster and sunflower and corn oils).

Most saturated fats come from animal and dairy products. Excess amounts can increase the risk of heart disease by raising our cholesterol levels.

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