While the low-fat diet craze led some doctors to worry that Americans would instead start eating too many carbohydrates, a new study suggests that eating low-fat doesn't have to increase carbohydrate-fuelled health risks.
Instead, if extra carbohydrates are part of a diet plan that includes more fruits, vegetables, and whole grains, the risk of diabetes - the biggest related health concern -could actually drop, at least in older women, according to the findings.
However, a low-fat, high-carbohydrate diet could create problems in people who already have diabetes, researchers caution.
Reduce the fat
"Generally when people reduce the fat in the diet they replace it with carbohydrates," study author Dr James Shikany said. "There was some concern that the increased carbohydrate intake might lead to if not increased diabetes itself... changes that over time could lead to diabetes."
"We had been telling women to decrease their fat intake for a long time and we really didn't know the possible effects this would have" on diabetes, added Dr Shikany, from the University of Alabama at Birmingham.
The results suggest that balancing both diabetes and other disease risks requires considering the kinds of carbohydrates, fats, and proteins we eat, researchers said, rather than just cutting back on one food group and eating more of another.
The study, published in the American Journal of Clinical Nutrition, included a group of about 2,300 postmenopausal women who were part of the Women's Health Initiative trial, which looked at the effect of diet and hormone therapy on disease risks.
About 900 of the women, selected randomly, were told to decrease their total fat intake so that fat accounted for about 20% of the calories in their diet. For a 4,200kJ diet, that would mean eating 44g of fat each day.
As part of the new diet, women were also told to increase the number of fruit, vegetable, and grain servings they ate, and they attended regular sessions with nutritionists to help them do that.
The other 1,400 women, serving as a comparison group, were not given any extra nutritional guidance or told to change their diet.
The researchers followed women for the next six years with surveys on diet and exercise and also tested their blood glucose and insulin levels.
Women in the low-fat group, on average, said they got between 25 and 29% of their kilojoules from fat in follow-up surveys. That compared to 36 to 37% in the group without a diet intervention.
US government guidelines suggest adults get between 20 and 35% of their kilojoules from fat.
The diet group also generally ate fewer total kilojoules and more fruits, vegetables, grains, and sugar than the comparison group, on average.
After 1 year, women on the low-fat diet had lost more weight than the comparison group and had bigger decreases in their blood sugar and insulin levels. By six years, the groups looked similar on those measures. That told researchers that the lower-fat, higher-carbohydrate diet hadn't increased women's chances of getting diabetes.
Increase in blood sugar levels
However, in women who already had diabetes at the start of the study, those on the low-fat diet had a larger increase in blood sugar levels in the first year compared to women who didn't change their diet. That could be because people with diabetes had lost the ability to process the extra carbohydrates, Dr Shikany said.
Carbohydrates are "obviously not a poison," said Dr David Jenkins, head of the Clinical Nutrition and Risk Factor Modification Centre at St. Michael's Hospital in Toronto. "If eaten wisely (they're) useful."
However, in general, "we went from a diet that was rich in saturated fat and cholesterol and was also not good (to) a diet which was equally tasty, but relying on refining the carbohydrates in a particular way" that ups the risk of obesity and diabetes, Dr Jenkins, who was not involved in the new research, told Reuters Health.
"Things have kind of changed, but there still are plenty of (doctors) who recommend low-fat diets and people who are on these diets," he said. "I certainly think it's a very safe diet, but the question is, is this the best diet?" said Dr Shikany.
Dr Mary Gannon, of the University of Minnesota, said that a diet lower in carbohydrates and higher in fat and protein may actually help people feel fuller sooner - which could lead to weight loss over time. In male patients with diabetes she has studied, men had the most improvement in diabetes markers when they got the smallest percent of their calories from carbohydrates.
Dr Shikany added that because the research was limited to women age 50 and up, his findings don't necessarily apply to men or younger women on a low-fat diet(Reuters Health/ May 2011)
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Diet and Nutrition