With commentary by Nicola Guess, PhD, RD, MPH, lecturer, Imperial College and Kings' College, London, and Fumiaki Imamura, PhD, investigator scientist, University of Cambridge.
Want to reduce your risk of getting diabetes? Or improve your blood glucose levels if you already have type 2 diabetes?
Swapping out some of your refined carbs and saturated fats with unsaturated—especially polyunsaturated fats found in vegetable oils and fatty fish—can help, according to new research.
Skip the pastries and white bread with butter, bring on the olive oil and salmon.
"Unsaturated fatty acids, including monounsaturated and polyunsaturated, are better than saturated fats or carbs for blood sugar control," says Fumiaki Imamura, PhD, an investigator scientist at the University of Cambridge and lead author of the new report, published July 19, 2016 in PLoS Medicine.1
''Among different fats, the most consistent benefits were seen for increasing polyunsaturated fats, in place of either carbohydrates or saturated fat," says Imamura. Polyunsaturated fats are found in plant-based oils such as olive, soybean, corn and sun flower, as well as salmon, mackerel and other fatty fish.
Imamura, joined by researchers from Tufts University and other universities, reviewed 102 randomized controlled trials, the gold standard for research, involving more than 4,000 men and women. In the original studies, the researchers provided foods to the participants and looked at how variation in the diet impacted blood sugar, insulin, insulin resistance and sensitivity and the body's ability to produce insulin in response to blood sugar.
Overall, for each five percent of calories switched from carbohydrates or saturated fat to monounsaturated or polyunsaturated fat, there was a .1% decline in A1C, a measure of blood sugar control over the previous three months, the researchers found.
That may not sound like much. However, based on other studies, experts estimate that each .1% drop in A1C can reduce the incidence of type 2 diabetes by 22% and the incidence of cardiovascular disease (which automatically rises if you have type 2 diabetes) by about 7%.
Experts know that fiber intake is important to keep blood sugar levels healthy, Imamura says. However, beyond that, the effects of dietary fat and carbohydrates on blood sugar and insulin sensitivity have been debated, he says. So, his team set out to conduct a thorough evaluation of the available evidence. Before conducting the review, Imamura says, the researchers had hypothesized that unsaturated fats were preferable to saturated fats or refined carbohydrates. As expected, he says, "we found monounsaturated or polyunsaturated are better than saturated fats and carbohydrates to keep glucose under control."
Based on the study findings, the researchers say that focusing on polyunsaturated fats in particular may help the body produce more insulin when it is needed.
The new findings echo some from research published earlier this year in PLos One, says Nicola Guess, PhD, RD, MPH, a lecturer at Imperial College and Kings' College, London, who led that study.2 With her colleagues, she evaluated 73 people, including athletes, obese adults, those with normal blood sugar, those with prediabetes or type 2 diabetes. Her findings support what the new research also shows, she says.
"The new study shows if you replace refined carbohydrates such as white flour or white rice, and saturated fat such as butter, with vegetable oils, avocados and nuts….it reduces the risk of getting type 2 diabetes," Guess says.
Different pathways may be at work, explaining why the unsaturated fats help reduce blood sugar, Guess says. "We found the vegetable oils and nuts seem to reduce diabetes risk by reducing blood sugar," she says. But her team also thinks those foods may help the muscles take up the glucose, she says.
Here's how to put the results to work. Remember that the new study found that switching just 5% of energy from carbs and saturated fat to healthier fats made a difference, Imamura says. So, ''for a 2,000-calorie diet, 5% is 100 calories," Imamura says. Practically speaking, look for ways to replace foods high in calories, saturated fat and carbs with foods that have fewer (or no) carbs and contain poly- or monounsaturated fat instead.
Some good swaps: "Have a handful of nuts instead of a full-fat yogurt," Guess says or, swap that butter for olive oil or vegetable oil.
One caveat, Imamura says. The studies reviewed included Western populations, mostly Caucasians. "So we are not sure if this finding can be translated to glucose control among Hispanic people for instance, or African Americans or Asians."
In general, however, the message from the new review is very positive, says senior author Dariush Mozaffarian, MD, DrPH, dean of the Tufts University Friedman School of Nutrition Science and Policy. "Don't fear healthy fats."
Editor's note: Dr. Mozaffarian reports honoraria or consulting from a variety of sources, including Haas Avocado Board.