If you're contemplating going on a diet or altering your eating habits - and you're a woman - beware the high protein mantra. While high protein diets have been shown to work for weight loss, protein - specifically animal protein - contains acid. When eaten in large amounts, without sufficient quantities of foods that neutralize the acid, the bones are affected. Scientists at the University of California, San Francisco (UCSF) found that women who eat more meat than vegetable protein have a higher incidence of bone loss and hip fractures than women who eat equal amounts of both types of food.

The researchers followed women because they are at higher risk for osteoporosis than men. In women, the hormone estrogen contributes to the bone-building process, so as estrogen levels fall when women approach menopause, their bone loss accelerates to a rate of 2% to 3% per year.

For 7 years the researchers at UCSF followed a group of 1,035 women aged between 65 and 80, all of whom are enrolled in the larger Osteoporotic Fractures Study currently taking place in the United States. The researchers found that the women who ate 4 times as much animal protein as vegetable protein had 3 times the rate of bone loss, and 3.7 times the rate of hip fractures compared to the women who ate equal amounts of both animal and vegetable protein. "Even after adjusting for all the things that could impact the relationship between high animal protein intake to bone loss and hip fractures, the relationship was still there," said Dr. Deborah Sellmeyer, one of the investigators involved in the study.

So how is the acid affecting the bone? Dr. Sellmeyer explained that our bones help to neutralize excess acid. "Our bodies don't like too much acid, so our kidneys excrete it in urine. As we get older, even if we are completely healthy, our kidneys become less efficient," she said. However, a substance called base, which is found in vegetables as well as bone, neutralizes acid. "If we don't get enough base in our diet - if we're not eating enough fruits and vegetables - our bones become involved in neutralizing the acid. Over time this leads to loss in bone mass and calcium. Consequently, eating more vegetables with our steaks and hamburgers will not only help neutralize the acid but also improve bone health.

"The message is that we need more base in our diets," Dr. Sellmeyer said. Rather than eating less animal protein, we should think of eating more vegetables.

"There is no doubt that protein is really important. Studies involving people who have had hip fractures have shown that if they receive supplemental protein in their diets after their fractures, they heal better, and they get back on their feet faster," Dr. Sellmeyer said. "We need protein, but we must neutralize the acid. The best way to do that is to eat more fruits and vegetables."

While women are obviously at higher risk for osteoporosis than men, men do suffer from this disease. Can a high protein diet have similar affects on men? "Men have a different risk factor profile from women. Being bigger and heavier, on average, they tend to have higher bone density. Whether they can withstand the acid load from high animal protein intake their whole lives without getting into trouble remains to be seen," said Dr. Sellmeyer. A study is currently underway to further explore the effects of acid on bone health in both men and women. In any event, it seems that expression "meat and 2 veg" is actually very sound dietary advice.


Claire Sowerbutt, medical writer 
in association with the MediResource Clinical Team