High-protein diets may be trendy, but the jury is still out on whether they're safe in the long term, according to the University of Maryland Medical School. In addition, cutting carbs does not guarantee weight loss. You burn fat when you consume fewer calories than you expend for energy, and high-protein diets were shown to be no more effective than other diets in a two-year study published in "The New England Journal of Medicine" in 2009.
Where's the Fiber?
Many protein sources, including meat, fish, eggs and dairy, don't contain any fiber. Only plant foods such as grains, fruits and vegetables contain fiber, and low-carbohydrate diets often lack these items. You need fiber for healthy digestion; without enough of this nutrient, your risk of constipation, hemorrhoids and other digestive troubles may increase. Fiber may also help manage cholesterol levels, reducing your risk of heart disease. Per the 2010 Dietary Guidelines for Americans, you should get about 14 grams of fiber for every 1,000 calories you eat, or 28 grams in a 2,000-calorie-a-day diet. High-protein fiber sources include beans and nuts.
The Ketosis Issue
On a low-carb diet, your body is forced to burn fat for fuel instead of carbohydrates. Some parts of your body, like your brain, can't use fat for energy, so your body must produce substances called ketones to supply them with fuel. Overproduction of ketones results in a condition called ketosis, which may cause bad breath, upset stomach, kidney stones and even kidney failure. In extreme cases, ketones cause the blood to become too acidic, resulting in brain damage and death.
Eating too much protein may lead to increased risk of death in middle age, according to a study published in "Cell Metabolism" in 2014. Researchers found that respondents between the ages of 50 and 65 who ate high-protein diets had a 75 percent greater risk of mortality from any cause and were four times as likely to die from cancer than those on low-protein diets. Only animal proteins, however, were associated with increased mortality; plant proteins were not.
Eating in Balance
The healthiest diet is a varied one that represents all major food groups. For optimal nutrition, the 2010 Dietary Guidelines for Americans recommends getting 45 to 65 percent of calories from carbohydrates, 10 to 35 percent of calories from protein and 20 to 35 percent of calories from fat. If you include meat and cheese in your diet, choose lean and low-fat options, as saturated fat from animal sources is linked to high cholesterol levels.