Low carbohydrate diets tend to contain disproportionate amounts of fat from animal sources. Red meat has long been vilified as a major source of saturated fat that some experts believe cause hardening-of-the-arteries (atherosclerosis) via elevations in LDL cholesterol. Others disagree. Poultry, fish ,and shellfish generally have lower amounts of saturated fat than red meat. Would a low-carb diet with a predominance of poultry, fish, and shellfish lead to a more advantageous cholesterol profile?
A 2007 report from U.S. researchers found no lipid advantage to the poultry/fish/shellfish model. In fact, despite high cholesterol and fat intakes, neither diet caused a significant change in total, HDL, or LDL cholesterol levels. Triglycerides fell in both groups, but to a statistically significant degree only on the poultry/fish/shellfish group.
Fun Fact: Did you know that four of every 10 women in the U.S. are trying to lose weight? The figure for men is one in three.
Researchers in Minnesota and Iowa enrolled 18 subjects (6 males, 12 females) between the ages of 30 and 50 who wanted to lose weight. Average body mass index was 31.7, which is mildly obese. The were encouraged to eat an Atkins-style ketogenic diet with a maximum of 20 g carbs/day, providing 1,487 total daily calories, with 7% of calories from carbohydrate, 43% from protein, and 50% from fat. This included two or three cups of salad greens and low-carb vegetables. Three ounces of cheese daily was allowed. Subjects were randomly assigned to eat either red meat or poultry/fish/shellfish. Dietary intervention lasted 28 days.
[This is very similar to Atkins Induction Phase, although Atkins does not limit total calories. The researchers did not say why they wanted to limit total calories.]
Data were not used from six subjects for good reasons (see article). So final data analysis included only 12 subjects.
Both groups lost the same amount of weight: about 5.5 kg (12 pounds) over 28 days.
Average carbohydrate intake was about the same for both groups: 55 g/day.
Average total daily caloric intake was about the same for both groups: 1,380.
The poultry/fish/shellfish group ate 630 mg cholesterol daily, twice as much as the other group. [Eggs and shrimp were popular.]
The difference in intake of saturated fat approached, but did not reach, statistical significance (32 g/day in the red meat group vs 25 g).
Neither diet caused a significant change in total, HDL, or LDL cholesterol levels. Triglycerides fell in both groups, but to a statistically significant degree only on the poultry/fish/shellfish group.
Urine ketones at or above 5 mg/dl were detected on 75% of all dipstick tests.
I’m skeptical about the accuracy of the calorie counts. Most people eating Atkins-style take in about 1,800 cals/day. The preponderance of females, however, may explain the unusually low average caloric intake. They didn’t follow their carb restriction very closely, did they? These were free-living subjects not locked in a metabolic ward.
The researchers note that the allowance of cheese in both groups may have sabotaged their efforts for a clear delineation of higher versus lower saturated fat groups.
HDL cholesterol usually rises significantly on low-carb diets. Lack of that here may just be a statistical aberration.
This is such a small study that it’s impossible to draw firm conclusions. Nevertheless, if someone is losing weight on a low-carb diet, it may not matter much from a lipid viewpoint whether they eat a predominance of meat or a predominance of poultry, fish, and shellfish. The study at hand cannot address the long-term consequences of such a choice.
Steve Parker, M.D.
Reference: Cassady, Bridget, et al. Effects of low carbohydrate diets high in red meats or poultry, fish and shellfish on plasma lipids and weight loss. Nutrition & Metabolism, 4:23 doi: 10.1186/1743-7075-4-23 Published October 31, 2007