Your body needs significant amounts of fat and carbs in your diet. Both are macronutrients, which provide energy but are markedly different nutrients with unique chemical compositions. When you consume each nutrient in your food, your body breaks them down differently and they go to different places where they serve different roles in energy metabolism.
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Absorption and Storage
Both fat and carbohydrates are important for storing energy. When you consume carbohydrates, your body breaks them down into glucose, which it uses to fuel energy metabolism. Unused glucose is transported to the liver, where it is stored for later use. Monosaccharides are broken down quickly and cause a sudden rise in blood glucose levels. Polysaccharides are absorbed more slowly and cause a gradual influence on blood glucose levels, generally making them a healthier food choice. Fat is broken down into smaller fatty acid molecules and cholesterol, where the blood carries them to different parts of the body for storage.
While both fat and carbohydrates are rich sources of energy, they serve several unique functions as well. Many vitamins are fat soluble and you need a sufficient amount of fat deposits to store and use the vitamins you eat. Fat also helps regulate hormone production and it insulates and protects vital organs. Carbohydrates provide both short-term and long-term energy when broken down into blood glucose or stored as glycogen, respectively. Fiber, a specific undigestible form of carbohydrate, can help maintain healthy blood glucose levels, cleanse the colon, lower blood cholesterol levels and reduce the risk of cardiovascular disease.
Carbohydrates should account for about 45 to 65 percent of your total caloric intake, according to the Food and Nutrition Board of the Institute of Medicine. If you consume a 2,000-calorie diet, you would need about 900 to 1,300 calories from carbohydrates or about 225 to 325 grams. Fat should account for about 20 to 35 percent of your calories. A 2,000-calorie diet should then be comprised of 400 to 700 calories from fat or 44 to 78 grams.
Making Wise Choices
When eating carbs there are some choices that are better than others. The Harvard Medical School recommends low-glycemic carbohydrates, which won't raise your blood sugar as quicky as high glycemic carbs. Good choices are fruits and vegetables, beans, nuts, low-fat dairy products, whole grains and whole-wheat pastas. When choosing fats, opt for mono- or polyunsaturated fats. Good fats include olive oil, sesame oil, safflower oil, walnuts, avocados, nuts, olives, flaxseeds and fatty fish.
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- Western Kentucky University Department of Biology: Carbohydrates
- National Digestive Diseases Information Clearninghouse: Your Digestive System and How it Works
- Institute of Medicine Dietary Reference Intakes: Macronutrients
- KidsHealth: Learning About Carbohydrates
- Harvard Medical School: Choosing Good Carbs With The Glycemic Index
- MedlinePlus: Fat
- Helpguide.org: Choosing Healthy Fats