July 31, 2014
News Review From Harvard Medical School -- Nuts May Help Lower Blood Sugar
Eating more tree nuts may help with diabetes control, a new review of research suggests. The study combined results from 12 previous studies. In those studies, people with type 2 diabetes were randomly divided into groups. One group ate more tree nuts and the other group did not. Both diets were equal in calories. On average, the amount of nuts added was 56 grams (about one-half cup). Usually, just one type of nuts was used. Tree nuts do not include peanuts. The studies were mostly short-term. On average, people who ate more nuts ended up with fasting glucose levels 2.7 milligrams per deciliter (mg/dL) lower than those on the other diets. The average hemoglobin A1C level was 0.07% lower for nut eaters. A1C measures blood-sugar control over about 3 months. The studies that showed the greatest reductions in blood sugar added nuts to replace some carbohydrates in the diet. The authors said most studies were of poor quality. The new study was funded by the International Tree Nut Council Nutrition Research & Education Foundation and the Canadian Institutes of Health. About half of the authors reported previous food-industry funding. PLoS One published the study online July 30.
By Robert H. Shmerling, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
It's not often that medical science discovers new health benefits for something you already like to do.
A new study that links eating nuts with positive effects on blood sugar is one example. Before you rush out to buy nuts, it's important to note the details of the research. The studies were limited to people with type 2 diabetes. The improvements were linked with eating more tree nuts, such as:
- Pistachio nuts
Peanuts are not on the list. That's because they are legumes, not tree nuts.
The new research is called a meta-analysis. That means it analyzed the results of previous studies. It included 450 people with type 2 diabetes. After about 8 weeks of eating more tree nuts:
- Those who ate about 2 servings (about one-half cup) each day had lower fasting blood sugar results and lower HbA1c levels than those who ate fewer tree nuts. Fasting blood sugar and HbA1c levels are common measures of diabetes control. In general, lower is better.
- Those who ate more tree nuts had lower insulin levels than those who ate fewer. They also had less insulin resistance. This means their bodies were better able to use insulin to move sugar out of the blood so it can be used for energy. The differences between groups were small enough that they could have been caused by chance. But these changes were positive ones because insulin levels tend to rise as insulin resistance increases in type 2 diabetes.
- The biggest improvements were noted when people ate tree nuts instead of carbohydrates.
This study is important because it provides people with type 2 diabetes a way to improve blood sugar and the body's use of insulin without adding a medicine. Given the rising number of people with type 2 diabetes, the impact of these findings could be big.
However, other questions remain. For example:
- How much of the improved blood sugar control was due to eating tree nuts, and how much was due to eating fewer carbohydrates?
- Which nuts provide the most benefit?
- Does a long-term increase in tree nut consumption come with any "side effects," such as weight gain?
- Will larger and longer-term studies confirm the findings of this new research?
What Changes Can I Make Now?
Preventing diabetes is the best way to prevent the further health problems it can cause. Maintaining a healthy weight and avoiding obesity are crucial first steps.
If you already have type 2 diabetes, this study suggests that eating 2 servings of tree nuts each day might help to improve your blood sugar. However, keep in mind that nuts are high in calories. Eating too many (for example, 3 or more servings per day) without adjustments in other foods could lead to weight gain. And weight gain can make diabetic control worse.
If you have diabetes, you can take other measures to control your disease and reduce the risk of further health problems.
- Exercise regularly.
- Meet with a nutritionist, and stick with a heart-healthy, diabetic diet
- Keep track of your blood sugar. Take medicines to lower it as prescribed.
- Take an aspirin each day. This helps to prevent stroke and heart attack, especially for those who have had these problems in the past.
- If you have high blood pressure, take a medicine to reduce it.
- Take a statin medicine. The goal cholesterol level for people with diabetes should be lower than for people without diabetes.
- Don't smoke.
Play an active role in your own care. For example, if you have kidney disease, make sure every doctor you see knows about it. Some medicines are dangerous when taken by a person with kidney disease. Doses of many medicines may need adjustment. Speaking up can prevent these kinds of problems.
What Can I Expect Looking to the Future?
In recent years, nuts have been featured more prominently in what is considered a "healthy diet." They are part of the Mediterranean Diet and the U.S. government's Dietary Guidelines. However, these diets do not distinguish between tree nuts and other nuts. And they don't recommend more nuts if you have diabetes. That could change in the future, especially if more research:
- Confirms the findings of this latest study.
- Identifies how tree nuts lower blood sugar. The authors speculate that the reduction in carbohydrates, the high magnesium content of nuts or the monounsaturated fats in nuts may be what improves blood sugar levels.
- Shows that eating tree nuts can actually prevent diabetes in those at risk.
If you like nuts as much as I do, you may want to eat more even before further studies have been completed. I know I will.