The study, conducted by the Antioxidants Research Laboratory at Tufts University in Boston, was conducted on 26 overweight or obese older adults aged 45 or older. The researchers chose otherwise healthy subjects who had a high waist to hip ratio, indicating central adiposity, which is a risk factor all its own.
The researchers used whole nuts as a major source of energy to substitute into a typical low-fiber, higher fat American diet. While tree nuts are generally thought of as a good source of fiber, the diets were standardized to the same levels of fiber overall as well as those of other macronutrients such as protein and carbohydrates.
The diet ratios looked like this: Each had slightly more than 2000 calories a day. Carbohydrates made up about 47-48% of overall intake, protein 15% to 16% and fat 35% to 36%. There were 1.1 servings of fruit and 2.3 servings of vegetables in both diets. Fiber intake in both cases was about 18 grams, which is less than the recommended 25 grams to 30 grams but represents the average American intake.
Parsing out the particular benefits
The consumption of tree nuts in general has been associated with health benefits. The researchers noted that previous research has shown a reduction in cardiometabolic risk factors when nuts are included in a low fat, high fiber diet. But those studies have also shown a greater benefit than one could attribute just to the nuts’ healthful mixture of fats, thus raising the question whether the tannic components of the foods could be contributing a synergistic effect.
“Other bioactive compounds present in nuts, including micronutrients, fiber, and phytochemicals, may also contribute to their cardio-protective effect by reducing inflammation, improving vascular reactivity as well as fasting glucose and insulin sensitivity, and by lowering oxidative stress status. Therefore, well-controlled studies focusing on the additive and/or synergistic effects of the nut constituents present in the whole food matrix, and the degree to which they confer a health benefit and prevent chronic disease, are warranted,” they wrote.
The researchers noted that there has been very little previous research done into the health benefits of pecans. A mere four studies come readily to hand, only one of which was done in the past 10 years.
The present study was a double blinded, placebo-controlled crossover design. The presence of the nuts were disguised with how they, or similarly textured ingrdients, were blended into the dishes prepared for the participants. All participants were asked to eat only the food prepared for them at the Tufts clinic. There were two four-week feeding phases, with a two week washout period in between. Participants were asked to continue with the ‘typical’ high fat, low fiber diet during the run-in and washout phases to reduce confounding factors.
Significant improvement in blood glucose markers
The researchers measured oxidative markets, blood lipid profiles. They also looked at markers of glucoregulation and insulin sensitivity. And they looked at a marker for beta cell function, which is a measure of insulin release in the pancreas. They found a statistically significant improvements for the pecan test diet on several parameters.
“After four weeks on a pecan-rich diet, changes in subjects’ serum insulin, insulin resistance (HOMA-IR) and beta cell function (HOMA-β) were significantly greater than on the control diet,” they wrote. Total and LDL cholesterol were lower on the test diet, too, but was on the borderline of statistical significance. The diets were designed to maintain body weight throughout the study.
Still a small portion of market
Pecans are borne on a tree of the hickory family (Carya illinoinensis) native to the lower Mississippi Valley, Texas and northern Mexico. They have been consumed by people living in the region, both Native Americans and the European settlers who displaced them, for thousands of years. But the nuts represent only a niche market when compared with intensively farmed competitors such as almonds.
Recent USDA data shows the utilized production of pecans on a shelled basis ranks behind almonds, walnuts and pistachios, sitting ahead of only macadamia nuts and hazelnuts. About 1.3 million pounds of shelled pecans were utilized in the 2016/2017 time frame. But the figure for almonds for the same period was 2.3 billion pounds. In fact the demand for almonds outstrips all of the other tree nuts combined, according to the USDA data.
That could be changing. Margaret Lisi, of the Center for Pecan Innovation in Atlanta, noted in 2015 that the consumption of pecans had jumped 10% from 2013 through 2014, and in fact the USDA tonnage data for those crop years bears this out. But the harvest shrank thereafter to a low of 1 million pounds in the 2014/2015 time frame before rebounding.
Increasing marketing efforts on behalf of pecans could in the future support increased acreage. In 2016 the industry got approval for a Federal Marketing Order that allows it to collect mandatory dues to support a new American Pecan Council, which will determine how the funds will be used. The current study was supported in part by a grant from the National Pecan Shellers Association.
A Pecan-Rich Diet Improves Cardiometabolic Risk Factors in Overweight and Obese Adults: A Randomized Controlled Trial
2018 Mar 11;10(3). pii: E339. doi: 10.3390/nu10030339
Authors: McKay DL, Eliasziw M, Chen CYO, Blumberg J