BOSTON -- Obese, postmenopausal women who adhered to a Paleolithic-type diet had improved biomarkers for insulin resistance compared with women on a low-fat diet, researchers reported here.
Among 70 women who were randomized to receive either a Paleolithic diet or a low-fat diet for 24 months, fatty acid and liver enzyme composition in the blood showed improved metabolic markers for lower insulin resistance, despite similar weight loss, Caroline Blomquist, a PhD candidate at Umeå University in Sweden, and colleagues, reported at the annual meeting of the Endocrine Society.
"A Paleolithic-type diet reduced specific fatty acids and desaturase activities in the blood, associated with insulin resistance, more distinctly than a control diet did, despite similar weight loss," Blomquist said in a presentation. "The Paleolithic-type diet may have long-term beneficial effects on obesity-related disorders such as insulin resistance and cardiovascular disease."
Estrogen decreases when women enter menopause, Blomquist said, leading to abdominal adiposity and increased insulin sensitivity. The mechanism at play with the Paleolithic diet, she added, was the pro-inflammatory factors stimulated by saturated fatty acids. "These proinflammatory factors can induce a low-grade inflammatory state in the body, resulting in decreased insulin sensitivity and cardiovascular diseases."
"Polyunsaturated fatty acids, from things like fish, can, on the other hand, have beneficial effects on insulin sensitivity by affecting specific genes, muscles, and the liver. Polyunsaturated fatty acids can also reduce inflammation and appetite," Blomquist said. "Dietary fatty acids influence adipose tissue function as well as whole body metabolism."
All 70 of the women in the trial were healthy, obese, postmenopausal, and had normal plasma glucose levels. For the Paleolithic diet, women were instructed to consume a diet consisting of 30% protein, 30% carbohydrates, and 40% fats, including a good amount of unsaturated fatty acids. The Paleolithic diet allowed for consumption of lean meat, fish, fruits, vegetables, oils, and nuts, but not dairy, cereals, added salt, or refined fat and sugars.
For the low-fat diet, women were directed to consume 15% protein, 55% carbohydrates, and 30% fat. These women were told to increase their intake of whole grains, to use low-fat dairy products, and to have three servings of fish per week.
At the 6-month mark, women in the Paleolithic group lost more weight compared with women in the low-fat group, but by 24 months, the weight loss was similar between the groups, at 11% for the Paleolithic group and 8% for the low-fat group.
Blomquist noted potential bias in self-report food intake, and the use of biomarkers to identify dietary adherence.
The fish intake increased in both groups, according to the biomarkers for unsaturated fatty acids, which has been associated with insulin sensitivity. But, according to the biomarkers, this intake slowly leveled off for the remainder of the trial, Blomquist said.
The biomarker for dairy showed a sharp decrease among women in the Paleolithic diet after the first 6 months, and a slight uptick by the end of the trial.
There was a decrease in delta-9-desaturase activity, a liver enzyme associated with liver fat, insulin resistance, and mortality: "We found the index for this enzyme was reduced in the Paleolithic diet group during the intervention period," Blomquist said.
Adherence to the Paleolithic diet was strongest until 6 months, with an increase in fish intake and a decrease in intake of dairy compared with baseline and with the low-fat diet group. The metabolic profile showed a decrease in risk for insulin resistance in members of the Paleolithic dietary group at the 6-month mark.
The women in the Paleolithic diet reported that over the course of the 24-month trial, their saturated fatty acid consumption fell by 19%, but their monosaturated fatty acid consumption increased by 47%, and their polyunsaturated fatty acid consumption increased by 71% (P<0.001).