High-protein, high-fat dietary patterns, when followed over the long term, are associated with increased risk of the following conditions:
1. Colorectal cancer. Colorectal cancer is one of the most common forms of cancer and is among the leading causes of cancer-related mortality. Long-term high intake of meat, particularly red meat, is associated with significantly increased risk of colorectal cancer. The 1997 report of the World Cancer Research Fund and American Institute for Cancer Research, Food, Nutrition, and the Prevention of Cancer, reported that, based on available evidence, diets high in red meat were considered probable contributors to colorectal cancer risk. In addition, high-protein diets are typically low in dietary fiber. Fiber appears to be protective against cancer.8
2. Heart disease. Typical high-protein diets are extremely high in dietary cholesterol and saturated fat. The effect of such diets on blood cholesterol levels is a matter of ongoing research. However, such diets pose additional risks to the heart, including increased risk for heart problems immediately following a meal. Evidence indicates that meals high in saturated fat adversely affect the compliance of arteries, increasing the risk of heart attacks.9
3. Impaired kidney function. High-protein diets are associated with reduced kidney function. Over time, individuals who consume very large amounts of protein, particularly animal protein, risk permanent loss of kidney function. Harvard researchers reported recently that high-protein diets were associated with a significant decline in kidney function, based on observations in 1,624 women participating in the Nurses? Health Study. The good news is that the damage was found only in those who already had reduced kidney function at the study?s outset. The bad news is that as many as one in four adults in the United States may already have reduced kidney function, suggesting that most people who have renal problems are unaware of that fact and do not realize that high-protein diets may put them at risk for further deterioration. The kidney-damaging effect was seen only with animal protein. Plant protein had no harmful effect.10
The American Academy of Family Physicians notes that high animal protein intake is largely responsible for the high prevalence of kidney stones in the United States and other developed countries and recommends protein restriction for the prevention of recurrent kidney stones.11
4. Osteoporosis. Very high protein intake is known to encourage urinary calcium losses and has been shown to increase risk of fracture in research studies.12,13
5. Complications of diabetes. In diabetes, kidney and heart problems are particularly common. The use of diets that may further tax the kidneys and may reduce arterial compliance is not recommended.
In people with diabetes, the safest approaches to preventing or slowing kidney problems include controlling blood glucose levels, blood pressure, and cholesterol and decreasing protein intake to low normal levels.14
While high-protein diets may carry potential health risks for anyone if maintained for more than a few weeks, they are especially risky for people with recurrent kidney stones, kidney disease, diabetes, osteoporosis, colon cancer, or heart disease.
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