In a study of 17 obese men, U.K. researchers found that a protein-heavy, low-carb diet created certain changes in the colon that could, over time, contribute to colon cancer risk.

The study looked only at short-term shifts in certain compounds that are byproducts of metabolism, and not actual disease risk. So it does not show whether high-protein diets really raise the risk of any colon diseases.

"The concern raised by our studies is that the risk of colorectal cancer might be raised by long-term adherence to diets that are high in protein and low in carbohydrate, especially fiber," senior researcher Dr. Harry J. Flint, of the University of Aberdeen.

So what does that mean for people who want to lose weight?

Diets relatively high in protein and lower in carbs have been shown to help heavy people shed pounds. Furthermore, as Flint and his colleagues point out, obesity is thought to be a risk factor for a number of diseases, including colon cancer.

"People should not be discouraged from losing weight, as this offers important health benefits," Flint said.

However, he added, they should make sure that any weight loss plan they follow includes adequate amounts of fiber. People should also be aware, Flint said, that a high protein intake over months to years might have ill effects in the colon.

The findings are based on 17 obese men who each followed three short-term diets: a one-week menu plan designed to maintain their weight; a four-week high-protein diet with moderate amounts of carbohydrates; and a four-week high-protein diet low in carbs.

On average, the study found, when the men were on the high-protein diets, they had higher levels of substances known as N-nitroso compounds, and certain other metabolites that have been linked to cancer.

From the April 4, 2011, Prepared Foods E-dition