How the Atkins diet could increase your risk of bowel cancer

New research has discovered a link between eating less carbohydrate and lower levels of a cancer-fighting chemical in the gut.

The acid, called butyrate, is produced by bacteria and helps kill off cancerous cells.

But researchers from Aberdeen's Rowett Research Institute found low-carbohydrate regimes - such as the Atkins - can cause a four-fold reduction in the cancer-fighting bacteria.

Professor Harry Flint, who led the research, said: "In the long run, it is possible that such diets could contribute to bowel cancer. It is a preventable disease, and there is evidence that poor diet can increase your risk."

The Atkins diet has helped celebrities such as Jennifer Anniston, Catherine Zeta-Jones and Renee Zellweger to stay slim.

It calls for a drastic cut in carbohydrate intake, including foods such as potatoes, fresh dairy products and alcohol. This lasts around two weeks, and most report a huge drop in weight at this time.

Carbohydrate levels are then slowly increased over the following weeks.

But Professor Flint said some dieters may be tempted to keep the level low, and risk a greater likelihood of bowel cancer.

In the study at the Rowett Institute, 19 obese men were given three diets containing different levels of carbohydrate: high, medium and low. Those on the high diet consumed 400 grams of carbohydrate daily - the level in an average diet.

On the low diet, the men consumed only 24 grams a day - a normal amount in low-carbohydrate diets. The second group saw a four-fold drop in the level of the cancer-fighting bacteria.

Prof Flint said: "The changes in butyrate production that we observed in this study are the largest ever reported in a human dietary trial."

He added it was likely the results, which were published in the journal Applied and Environmental Microbiology, would be the same in women.

The low-carb craze took off in the late 1990s. Dr Robert Atkins published his book Dr Atkins New Diet Revolution and other health experts soon followed suit.

The Atkins diet is based on the theory that cutting carbohydrates switches the body's chemistry, turning it from a carbohydrate-burning machine to one that burns fat.

Dundee University's Professor Annie Anderson, nitritional advisor to Bowel Cancer UK, said: "Compared to other low-fat diets, there is little merit in low carbohydrate diets, apart from the fact that they can help people to lose weight.

"There are no long-term benefits to cutting down on fruits and fibre - for example in bread - and, as this report shows, doing so is likely to have a negative impact on your bowel health and may increase your risk of bowel cancer."

Low-carbohydrate diets have long been controversial. Supporters point to studies which show the diet's effectiveness when compared to other approaches to weight loss.

But criticisms include increased risk of heart disease, increased risk of the bone disease osteoporosis in women, and high cost.

One study blamed the Atkins diet for triggering an epidemic of constipation which researchers said could lead to bowel cancer.

It said Atkins could result in a range of bowel problems, people taking time off work sick and a reduced sex drive.

One specialist said the risk of bowel cancer increased when people ate a lot of animal fat and there was slow moving transit of food through the gut.

And he said a healthy diet involved eating much more fibre than Atkins allows. For the first fortnight, dieters are only allowed one and a half slices of bread a day - 18 per cent of the receommended amount of fibre if brown or only 3 per cent if white.

Dr Emma Knight, science information manager at Cancer Research UK, said: "We know that diet, body weight and physical activity can all influence our risk of developing bowel cancer.

"We recommend eating a healthy, balanced diet that is high in fibre, fruit and vegetables, and low in red and processed meat.

"Maintaining a healthy body weight is also important - getting enough physical activity will help as exercise reduces bowel cancer risk in its own right."