A low-carb diet is a common strategy for losing weight. Reducing your carb binging forces your body to burn fat for energy and helps you to squeeze into those expensive skinny jeans. Burning muscle tissue only occurs in extreme situations, like when there’s nothing else for your body to use for energy. Eating enough protein and fat on a low-carb diet should prevent muscle loss.
The amount of carbohydrates recommended for adults ranges from about 100 to 180 grams daily, depending on your size and activity level. A low-carb diet typically involves eating less than 70 grams of carbohydrates daily, but it can be as few as 10 grams a day for short periods of time -- it depends on the diet. However, a low-carb diet doesn’t usually mean low-calorie, because protein and fat intake are supposed to increase to compensate for the lost calories from carbs. So instead of getting about 60 percent of your daily calories from carbs, 25 percent from fat and 15 percent from protein, a low-carb diet may provide 40 percent from carbs, 30 percent from fat and 30 percent from protein. Think of low-carb diets as high-protein meal plans.
On a low-carb diet, your body may be forced to burn fat for energy if you are active enough or if your carb intake is low enough. Dietary sources such as animal fats and plant oils are burned first, but if they are not sufficient to maintain your activity level and if you’re carrying a few extra pounds, then your body will burn stored adipose tissue for energy. Burning fatty acids produces ketones, which your body and brain can use for energy instead of glucose. Ketones are energy efficient, as they produce about 12 percent more energy than an equal amount of glucose. On the downside, if your body isn’t very efficient at burning ketones for energy and too many build up in your bloodstream, a condition called ketosis can develop, which is characterized by dizziness, weakness, nausea and mood swings.
When you eat protein, your body reduces it into amino acids, which are absorbed and used to build or repair muscle, skin, hair and enzymes. If the amount of carbs and fat in your diet is not enough to meet your energy demands and there is no extra glycogen or body fat to burn, then your body can convert amino acids from food into glucose fuel. This is not the preferred pathway to make energy, but your body can adapt to it. Your body will use the amino acids from protein-rich animal and plant foods before it starts to break down its own structures.
Burning the protein in your muscles for fuel is not something that happens on the typical low-carb diet. However, if you’re eating very few carbs, fat and protein -- in other words you’re starving yourself -- and you have no excess glycogen or adipose tissue stored in your body, then your body will metabolize muscle tissue as a last resort to meet your basic energy needs. Suddenly switching to a low-carb diet may not give your body enough time to adapt to burning fat, and your energy levels may plummet, which can prevent you from working out and building muscle. If you’re a serious athlete, your lean muscle mass and strength may drop a little until your energy levels rebound. But for the average gal trying to get a little fitter and lose some weight, most moderately low-carbohydrate diets won’t make your muscles disappear. Of course, challenging your muscles at the gym with some weights will prevent atrophy too.
- Contemporary Nutrition: Functional Approach; Gordon M. Wardlaw et al.
- Human Metabolism: Functional Diversity and Integration; J. Ramsey Bronk
- Exercise Physiology: Energy, Nutrition, and Human Performance; William D. McArdle et al.
Sirah Dubois is currently a PhD student in food science after having completed her master's degree in nutrition at the University of Alberta. She has worked in private practice as a dietitian in Edmonton, Canada and her nutrition-related articles have appeared in The Edmonton Journal newspaper.