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High protein, low carbohydrate diets

High-protein, low- carbohydrate diets have been widely promoted in recent years as an effective approach to losing weight. These diets generally recommend dieters receive 30% to 50% of their total calories from protein. By comparison, the British Nutrition Foundation recommends a diet in which a smaller percentage of calories are derived from protein (nutrients essential to the building, maintenance, and repair of tissues in the body).

How do these diets work?

By drastically restricting carbohydrates to a mere fraction of that found in the typical diet, the body goes into a different metabolic state called ketosis, whereby it burns its own fat for fuel, producing little carbon fragments (called ketones) as a by-product. Normally the body burns carbohydrates for fuel -- this is the main source of fuel for your brain, heart and other organs. When the body is in ketosis, you tend to feel less hungry, and therefore you're likely to eat less than you might otherwise. However, ketosis can also cause health problems, such as kidney failure (see below).

As a result, your body changes from a carbohydrate-burning engine into a fat-burning engine. So instead of relying on the carbohydrate-rich items you might typically consume for energy, and leaving your fat stores just where they were before (alas, the hips, tummy and thighs), your fat stores become a primary energy source. The purported result is weight loss.

What are the health risks associated with high protein, low carbohydrate diets?

These diets can cause a number of health problems, including:

  • Kidney disease. Consuming too much protein can put a strain on the kidneys, which can make a person susceptible to kidney disease.
  • Cholesterol. Debate continues about the effects on cholesterol of a high protein diet. Some research suggests it lowers cholesterol in the short-term and may even raise levels of HDL (good) cholesterol. However, research of more than 43,000 Swedish women, and published in the British Medical Journal, found that the lower the intake of carbohydrates and the higher the intake of protein, the greater the risk of heart and cardiovascular disease.
  • Bones and kidney stones. High protein diets have also been shown to cause people to excrete more calcium than normal in their urine. Over a prolonged period of time, this can increase a person's risk of kidney stones. A diet that increases protein at the expense of a very restrictive intake of plant carbohydrates may be bad for bones, but not necessarily a high protein intake alone.
  • Cancer. One of the reasons high protein diets increase the risks of certain health problems is because of the avoidance of carbohydrate-containing foods and the vitamins, minerals, fibre and anti-oxidants they contain. It is therefore important to obtain your protein from a diet rich in whole grains, fruit and vegetables. Not only are your protein needs being met, but you are also helping to reduce your risk of developing cancer.
  • Unhealthy metabolic state (ketosis). Low carbohydrate diets can cause your body to go into a dangerous metabolic state called ketosis since your body burns fat instead of glucose for energy. During ketosis, the body forms substances known as ketones and prolonged ketosis can cause liver and kidney damage. Ketones can also dull a person's appetite, cause nausea and bad breath.

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