A handful of pecans a day may reduce biomarkers related to type 2 diabetes, according to a placebo-controlled, crossover study from Tufts University, published in March 2018 in the journal Nutrients. The study included 26 generally healthy but overweight or mildly obese middle-aged and older adults with excess belly fat.
For four weeks each, the participants ate a version of a typical American diet (low in fruits, vegetables, fiber, and “good” fats and high in low-nutrient, energy-dense foods)—one with pecans and one without. Both diets had the same amount of calories and fiber and the same proportion of total fat (35 to 36 percent of calories), carbohydrates (47 to 48 percent of calories), and protein (15 to 16 percent of calories); no alcohol was allowed. The nuts were added in place of some sources of saturated fat.
The pecan-rich diet—which included about 1½ ounces of pecans a day, or 15 percent of total calories—was associated with a significant reduction in several markers of metabolic function, including insulin levels, insulin resistance, and beta cell function (the ability of pancreatic cells to store and release insulin), compared to the pecan-free (control) diet. Unlike other nut studies, this one did not find a significant effect of pecans on blood cholesterol, but the researchers attributed this possibly to the lower amount of nuts used or to the high rates of obesity in the population.
Though the mechanism isn’t clear, pecans, like other tree nuts and peanuts (technically legumes, not true nuts), contain mono- and polyunsaturated fats (oleic and linoleic acid), fiber, minerals (including magnesium, manganese, copper, and zinc), phytochemicals (including phenols and proanthocyanidins), and other compounds (like phytosterols) that may together have protective effects.
Many previous studies have focused on the beneficial effects of all kinds of tree nuts and peanuts on blood lipids and glycemic control, and have linked nuts to better heart health. For instance, an analysis of 20 studies in BMC Medicine in 2016 linked consumption of just 1 ounce of nuts (tree nuts or peanuts) a day to a 29 percent decreased risk of heart disease, among other positive findings. But few studies have addressed these metabolic risk markers, or pecans in particular.
Don’t just add pecans (or other nuts) to your diet: Eat them in place of less healthful foods that are high in calories.
A version of this article first appeared in the UC Berkeley Wellness Letter.