Thursday, June 23, 2011

Low-carb, high-protein eating may curb cancer risk

Hitherto known mostly as a weight-loss method, low-carb eating may also protect us against cancer. A new study highlights how heavy intakes of sugar and refined carbohydrates typical of the industrialised Western diet could be a factor fueling the worldwide cancer epidemic.

The study, published next month in Cancer Research, indicates that eating a low-carbohydrate, high-protein diet may reduce the risk of cancer and slow the growth of tumors already present.

Although the study was conducted in mice, its authors said the findings are relevant to humans:  “The fact that human blood glucose can be significantly reduced with low-carbohydrate diets, and the association of many cancers with high blood glucose levels, suggest that our findings are very relevant to human cancers, particularly cancers that have been associated with higher blood glucose and/or insulin levels, such as pancreatic, breast, colorectal, endometrial and esophageal cancers.”

Cancer cells need significantly more glucose than healthy cells to grow and thrive. Restricting carbohydrate intake can significantly limit blood glucose and insulin, a hormone that is released in response to rising blood glucose and that promotes tumor growth in both humans and mice.

For the study, Gerald Krystal of the British Columbia Cancer Research Centre and his team implanted various strains of mice with human or mouse cancer cells and assigned them to one of two diets. The first diet, a typical Western diet, contained about 55% carbohydrate (mostly sucrose, or table sugar), 23% protein and 22% fat. The second contained 15% carbohydrate (mostly in the form of starches that were about 70% amylose, a more slowly digested sugar typically found in whole grains, legumes, bananas, sweet potatoes, radishes and parsnips), 58% protein and 26% fat.

The low-carb mice exhibited lower blood-glucose and insulin levels and their tumor cells grew consistently slower than in those fed the high-carbohydrate western diet. They also had lower lactate levels – a chemical that fuels cancer growth and metastasis.

In addition, mice genetically predisposed to breast cancer were put on the two diets and almost half of those on the Western diet developed breast cancer within their first year of life while none on the low-carbohydrate, high-protein diet did. Only one mouse on the Western diet reached a normal life span (approximately two years), with 70% dying from cancer. Only 30% of those on the low-carbohydrate diet developed cancer and more than half of them reached or exceeded their normal life span.

In addition to lowering blood glucose levels, a low-carbohydrate, high-protein diet can both boost the immune system’s ability to kill cancer cells and prevent obesity. “Certain amino acids (i.e., arginine and tryptophan) play a very important role in allowing killer T cells to kill tumor cells,” says Krystal.

Moreover, high protein diets lead to more rapid satiety, which reduces obesity. “Obesity has a dramatic effect on cancer incidence, likely, at least in part, by increasing chronic inflammation,” he explains.

All this doesn’t mean we need to banish carbohydrates forever; however, we need to differentiate between less-healthy carbohydrates that cause a sharp increase in blood glucose and healthier carbs with a gentler glycemic impact.

The former include starchy foods like baked goods made with white flour, potatoes and white rice – all of which make up a large proportion of the calories a typical Westerner eats every day.

The latter tend to be unrefined, natural foods such as vegetables, fruits, legumes, nuts or whole grains that are converted more gradually into blood glucose. (Similar to the carbs the healthier mice ate.) These foods also generally contain important anti-cancer plant chemicals; thus they play an important role in an anti-cancer diet. In Zest for Life I recommend that people stick to low-glycemic carbohydrates – especially non-starchy vegetables – and eat protein with every meal to keep blood glucose levels stable.

Does increasing protein intake mean eating more meat? Such a conclusion could be problematic, for red and processed meats are thought to increase the risk of colorectal cancer. (See this post.) My view is that we should eat some high-quality protein at every meal, but should aim to vary its sources as much as possible, alternating between fish, white and occasional red meat, eggs, legumes, nuts and minimally processed soy foods; Dr Krystal  uses whey protein isolate powder to boost his protein intake.

It’s worth noting that the low-carb, high-protein diet tested in this study is also low in fat (26%, as compared with around 35% in the traditional Mediterranean diet and 50% in the Atkins diet).  While hungry, captive mice will eat this kind of diet, humans struggle to stick to low-carb, low-fat diets for long. (A recent survey found that 80% of Dukan dieters regained the weight they had shed on this low-fat, high-protein regimen within three years.)

“It is likely that we could still attain very beneficial effects if we raised the fat slightly and reduced the protein slightly,” says Dr Krystal. Such a diet (say 20% carbohydrate, 40% fat and 40% protein) would also be easier to maintain than the 15% carb, 25% fat and 60% protein model used in the mouse studies, he says.

Again, the ancestral Mediterranean diet may offer the best solution: it is rich in low-glycemic vegetables and fruits, provides plenty of protein through fish, lean meat, legumes and nuts, offers healthy fats in the form of olive, nut and fish oils and is low in sugar and refined grains.

Best of all, it is simple and tasty, making it a pleasure to follow long-term.

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