The heavyweights of the nutrition arena, carbohydrates, fats and protein, are classified as macronutrients. Providing your daily energy supply, these are the three main sources of calories, and they also serve important functions in your body. Fat is the most energy-dense of the bunch, providing nine calories per gram. Carbs and proteins have less than half that, with four calories per gram. For optimal health, consume 45 to 65 percent of your calories from carbs, 10 to 35 percent from protein and 20 to 35 percent from fat.
Carbohydrates fuel your activities, converting to glucose in your body for immediate energy. Carbs you don't use right away may be stored in your muscles as glycogen and tapped for energy when you need it. Excess carbs may also be stored as fat. Although there are plenty of carbs in refined grains and sweets, the Dietary Guidelines for Americans 2010 recommend getting them from fiber-rich sources, which are less processed and more nutritious. Healthy grain sources include whole-wheat bread, popcorn, brown rice, buckwheat noodles and oatmeal. Fruits and vegetables are also nutritious carb options. If you follow a typical 2,000-calorie diet, you need 225 to 325 grams of carbohydrates per day.
Fat is vital for absorption of fat-soluble vitamins A, E, D and K, and also helps maintain mood and keep your mind sharp. Saturated fats and trans fats are the bad guys of the fat world, contributing to high "bad" LDL cholesterol. Saturated fats are found in egg yolks, red meat and fatty dairy. Monounsaturated and polyunsaturated fats are the good fats, contributing to healthy cholesterol levels and fighting inflammation. Ninety percent of your fats should be unsaturated -- get them from nuts, seeds, avocados and olive oil. For a 2,000-calorie diet, fit in 44 to 78 grams of total fat per day.
You need protein for healthy muscles, bones and skin -- in fact, every cell in your body has the stuff. Proteins are made up of amino acids, but only animal products contain all of the essential ones, making them complete proteins. Non-meat eaters can get complete proteins from eggs and dairy, but vegans must eat plant foods with complementary proteins, such as beans and rice. These foods each provide the amino acids that the other lacks. Soy and quinoa are exceptions -- they're both complete-protein plant foods. On a 2,000-calorie diet, you need about 50 to 175 grams of protein per day.
As necessary as macronutrients are, your body stores the excess as body fat, leading to weight gain. Women between the ages of 19 and 30 need about 2,000 to 2,400 calories per day to maintain weight, depending on activity level. Women ages 31 to 50 need between 1,800 and 2,200 calories per day. For every 3,500 extra calories you eat, you'll gain a pound of fat. That may seem like a lot of calories, but they can add up quickly -- consuming 500 extra calories per day will make you gain a pound per week.
- World Health Organization: Macronutrients
- Drugs.com: Food Label Reading
- MayoClinic.com: Healthy Diet: End The Guesswork with These Nutrition Guidelines
- Centers for Disease Control and Prevention: Carbohydrates
- HelpGuide.org: Choosing Healthy Fats
- MedlinePlus: Dietary Proteins
- FamilyDoctor.org: Nutrition - Determine Your Calorie Needs
- American Family Physician: Soy - A Complete Source of Protein
- HelpGuide.org: How to Lose Weight and Keep it Off
Nina K. is a Los Angeles-based journalist who has been published by USAToday.com, Fitday.com, Healthy Living Magazine, Organic Authority and numerous other print and web publications. She has a philosophy degree from the University of Colorado and a journalism certificate from UCLA.