Friday, April 14, 2006
Genes Linked to Obesity
The first common genetic variant that substantially increases a person’s risk of obesity has been identified, researchers claim. They hope that their discovery will open doors to new treatments for the condition.
The team identified a small genetic change in a region of DNA near a gene known as INSIG2 as being linked to obesity. DNA code is made up of four bases, or "letters". A single change in this particular region, from a G to a C, makes a person more prone to obesity, according to the study.
They believe this change somehow affects the regulation of the gene INSIG2, which has a role in fat production.
The US researchers, led by Albert Herbert at the Boston University Medical School, found that an individual with two copies of the C variant is 22% more likely to have a body mass index (BMI) greater than 30 – the point where people move from being "overweight" to "obese".
This is the first study to strongly identify a genetic component in obesity in a number of populations, comments Carol Shoulders at Imperial College London, UK.
More than one-third of people in the US are obese and other countries’ populations are increasingly facing similar weight issues. Scientists predict that genes may contribute anywhere from 30% to 70% of the risk of obesity, but they stress that environmental factors, like diet, play a crucial role.
Herbert and colleagues looked at almost 87,000 points in the human genome which show variation between individuals, and related this to the BMIs of over 900 people. They studied families from a long-running coronary study in Massachusetts, called the Framingham Heart Study.
The team found that one particular genetic variation near the INSIG2 gene correlated well with obesity.
In follow-up studies involving about 9000 individuals in total, they found the same association. The C variant was found to increase the risk of obesity in populations including people of Western European ancestry, African Americans and children. About 10% of populations they studied carried two copies of this mutation.
Herbert notes that the C variant did not show a strong influence on obesity risk in a population of nurses they also examined. He says that this might be because nurses concerned about maintaining a healthy weight were more likely to participate in the study.
People with two copies of the C variant were about 1 BMI unit heavier than other individuals – a relatively small difference in weight – than those with one or no copies of this variant. This underscores the idea that the genetic variant simply tips people from overweight to obese, believes Shoulders.
Journal reference: Science (DOI: 10.1126/science.1124779)
Tuesday, April 11, 2006
Vegan Weight Loss
April's Nutrition Reviews has an article about vegetarian diets and weight loss. In short, if you want to lose weight loss the critters from your diet. Vegetarian populations are slimmer than omnivores; and the experience lower rates of heart disease, diabetes, high blood pressure, and other life-threatening conditions linked to overweight and obesity. Compiling data from 87 previous studies, the review shows the weight-loss effect does not depend on exercise or calorie-counting, and it occurs at a rate of approximately 1 pound per week. That'll take the burger out of your hand. Consider this: its cheaper to lead a vegetarian diet and by making this switch you could drop 50lbs. per year. The other day we did a grocery run. My wife and I buckled out knees with the amount of food we brought in. How did we get some much food with $200? Three of the items were meat and two items were dairy. Vegetables are cheap.
In vegetarians, obesity prevalence ranges from 0 percent to 6 percent, note study authors Susan E. Berkow, Ph.D., C.N.S., and Neal D. Barnard, M.D., of the Physicians Committee for Responsible Medicine (PCRM).
The authors found that the body weight of both male and female vegetarians is, on average, 3 percent to 20 percent lower than that of meat-eaters. Vegetarian and vegan diets have also been put to the test in clinical studies, as the review notes. The best of these clinical studies isolated the effects of diet by keeping exercise constant. The researchers found that a low-fat vegan diet leads to weight loss of about 1 pound per week, even without additional exercise or limits on portion sizes, calories, or carbohydrates.
"Our research reveals that people can enjoy unlimited portions of high-fiber foods such as fruits, vegetables, and whole grains to achieve or maintain a healthy body weight without feeling hungry," says Dr. Berkow, the lead author.
"There is evidence that a vegan diet causes an increased calorie burn after meals, meaning plant-based foods are being used more efficiently as fuel for the body, as opposed to being stored as fat," says Dr. Barnard. Insulin sensitivity is increased by a vegan diet, allowing nutrients to more rapidly enter the cells of the body to be converted to heat rather than to fat.
Earlier this month, a team of researchers led by Tim Key of Oxford University found that meat-eaters who switched to a plant-based diet gained less weight over a period of five years. Papers reviewed by Drs. Berkow and Barnard include several published by Dr. Key and his colleagues, as well as a recent study of more than 55,000 Swedish women showing that meat-eaters are more likely to be overweight than vegetarians and vegans.