How Do Carbohydrates Convert to Fat?

Sugar turns into fat when an excess amount is consumed. While carbohydrates are the body's main energy source, it's important to eat the healthy complex variety and limit the unhealthy simple variety to avoid weight and fat gain.

Limit unhealthy varieties of carbs in order to avoid fat gain. (Image: Eugene Mymrin/Moment/GettyImages)

Tip

High amounts of unhealthy carbohydrates, such as sugary foods and refined grains, are transformed to triglycerides and stored as fat.

How the Body Uses Carbohydrates

When you eat carbohydrates, your digestive system breaks down sugars and starches into glucose, which is used for energy. The energy fuels physical activity and physiological functions, such as breathing and maintaining body temperature, says Oklahoma State University. In addition, glucose is the sole source of energy for the brain, nervous system and developing red blood cells.

Excess glucose is stored as glycogen. As blood glucose levels drop, the body breaks down glycogen to provide glucose. Glycogen reserves are only large enough to supply half a day of energy needs, so you need a frequent intake of carbohydrates, notes Oklahoma State.

Some parts of the body can use fat as a source of energy, but the brain, nervous system and red blood cells can't. If your carbohydrate intake is too low, protein in muscles is broken down to produce glucose to fuel these body parts. When this happens, the depletion of protein in muscles can result in muscle loss.

How Sugar Turns Into Fat

When high amounts of unhealthy carbohydrates are consumed, they're converted to triglycerides, a form of fat, and are stored in fat tissue, states the National Council on Strength & Fitness. The glucose-to-triglycerides pathway results in fat accumulation, which has fueled the low-carb craze.

Although excess carbohydrates are stored in humans as fat, it's important to note that this effect is associated with simple carbohydrates rather than complex carbohydrates. Simple carbohydrates consist of sugars and refined grains, while complex carbohydrates consist of vegetables and whole grains.

Since excess sugar turns into fat, you should limit your intake of refined carbohydrates, advises the NCSF. Conversely, reducing the intake of total carbohydrates or complex carbohydrates leads to the loss of protein and can culminate in dehydration and other ills.

The conversion of carbohydrates to triglycerides increases the risk of developing heart disease. High triglycerides are associated with arterial plaque buildup and blood vessel damage. It's also linked to a higher likelihood of blood clots, notes the NCSF.

Use of Fats for Energy

Like carbohydrates, fats are an essential nutrient needed for multiple body functions, including energy. MedlinePlus reports that, during exercise, the body first uses calories from carbohydrates. After 20 minutes, calories from fat begin to be used to supply the energy required for physical activity.

The University of Utah Genetic Science Learning Center says that 80 to 85 percent of the body's energy reserves are in stored fat. While the brain needs glucose from carbohydrates to use as fuel, the muscles and liver prefer to use fat as their energy source. Between meals, fat is slowly released from storage sites to fuel the cells.

A certain supply of fat is beneficial because it provides energy reserves when you don't have time to eat. Fat reserves are particularly important during illness, because they give the immune system the energy required to fight infections, states the GSLC. However, the benefits of fat reserves are outweighed by liabilities when too much fat is stored.

Use of Proteins for Energy

Proteins, made of building blocks called amino acids, have an array of functions that include transporting biological molecules, enabling communication between cells and catalyzing chemical reactions, notes the American Diabetes Association. When a person's diet is low in carbohydrates and fats, proteins can also serve as an energy source.

The American Council on Exercise says that protein is converted to glycogen for energy after athletes engage in moderate- to high-intensity workouts for an extended period. To spare your reserves of protein for other purposes, such as repair of damaged tissue, ACE advocates either replenishing your intake of carbohydrates during rigorous workouts or limiting your exercise sessions to 45 to 50 minutes.

Putting It All Together

Carbohydrates, fats and proteins are all essential for energy and a healthy diet, but each nutrient has healthy and unhealthy options. For optimal wellness, choose the recommended daily servings of nutritious foods within each category.

The Dietary Guidelines for Americans notes that carbohydrates should comprise 45 to 65 percent of your daily caloric intake. Pick carbohydrates that are plentiful in fiber, vitamins and minerals. The American Heart Association advocates eating five servings daily of vegetables and four servings of fruits. Also, try to eat three to six daily servings of whole grains such as oatmeal, brown rice, millet, barley and whole-wheat bread and pasta.

Limit sugary beverages, sweets and refined grains like white rice and white bread. The majority of "goodies," including cookies, cakes, pies and crackers are refined carbohydrates, which should be saved for special treats and not eaten regularly.

The United States Department of Agriculture advises limiting saturated fat consumption to less than 10 percent of your daily caloric intake. Rather than eating a low-fat diet, up to 35 percent of daily calories can come from fat. Just remember to make fat choices that promote wellness.

Healthy food sources of fat include fish varieties like salmon and lake trout, which are rich in omega-3 fatty acids, states the Academy of Nutrition and Dietetics. Other good picks are avocados, nuts and olive oil, which contain monounsaturated fat. Peanut butter is also healthy, but select a brand that doesn't have added sugar. Avoid hydrogenated oils, which are found in shortening and margarine.

The American Cancer Society lists healthy protein foods as eggs, beans, nuts, seeds, fatty fish, poultry and lean meats. Eats one to two servings per day. Limit red meats, such as beef, pork and lamb, which are high in saturated fat. Avoid processed meat, including deli meats, hot dogs, sausage, ham and bacon, because a June 2017 review by the World Cancer Research Fund International concluded than the foods were linked to colorectal cancer.

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