Insulin-resistance, low magnesium intake linked
Another facet in the diabetic’s diet
Low magnesium intake appears to contribute to insulin resistance, say Pennsylvania researchers after studying 179 young black Americans.
The study’s lead author, Suzanne Humphries, MD, a former fellow in nephrology at MCP Hahnemann University in Philadelphia, hypothesizes that the results may apply to anyone who fails to get the recommended daily allowance of magnesium (410 mg per day for men and 315 mg for women). (See chart, below.) This is due to the critical role magnesium plays in carbohydrate metabolism, which is impaired in diabetics.
| Magnesium Content of Foods | ||
| Food | Amount | Magnesium |
| Halibut | 3 oz | 90 mg |
| Toasted almonds | 1 oz | 86.46 mg |
| Brown rice | 1 cup | 85 mg |
| Nigari tofu | ½ cup | 57.96 mg |
| Yogurt, nonfat | 1 cup | 46.79 mg |
| Skim milk | 1 cup | 39.5 mg |
| Whole grain cereal | ½ cup | 39.5 mg |
| Banana | medium | 34.2 mg |
| Salmon | 3 oz | 24.6 mg |
| Whole wheat bread | 1 slice | 24 mg |
| Catfish, fresh | 3 oz | 23.8 mg |
| Tuna, canned in water | 3 oz | 22.9 mg |
| Ground beef, extra lean | 4 oz | 22.6 mg |
| Broccoli | ½ cup | 18.72 mg |
| White rice | 1 cup | 18 mg |
| Grapefruit | ½ large | 13.28 mg |
| Carrots | ½ cup | 10.14 mg |
| Cheddar cheese | 1 oz | 7.87 mg |
| White bread | 1 slice | 6 mg |
| Source: U.S. Department of Agriculture Nutrient Database. Web site: www.nal.usda.gov/fnic/cgi-bin/nut_search.pl | ||
The study, published in the August issue of the American Journal of Hypertension, showed an average daily magnesium intake of 202 mg, less than two-thirds of the recommended daily allowance (RDA) for women and less than one-half the RDA for men. While Humphries and her colleagues found no association between blood pressure and magnesium intake in the study subjects, "The clinical onset of diabetes often precedes that of hypertension, and so this result in our sample of relatively young adults was not unexpected," she wrote.
Humphries, who is now assistant professor of nephrology at the University of Medicine and Dentistry at Cooper Hospital in Camden, NJ, says changes in membrane permeability might be part of the reason for the insulin resistance in her subjects. The primary culprit in the magnesium deficiency: "Their diets were so terrible. They were people who don’t have access to good food or don’t even know what it is. Some were getting as much as 10 g of sodium in a day." The typical American diet, she says, is low in magnesium-rich foods such as whole grains, cereals, and nuts.
While Humphries says there is not enough evidence from this relatively small study to warrant a blanket recommendation to check magnesium levels, clinicians would do well to advise patients to increase their intake of whole, unprocessed foods and avoid processed foods and refined flours.
The best sources of magnesium come in whole grains, dairy products, fruits, seafood, and meat, says Jeannette Jorden, RD, CDE, a spokeswoman for the American Dietetic Association. In addition, she is prevention, detection, and education coordinator for the Medical University of South Carolina in Charleston.
She advises health care professionals see their patients get two to three servings of dairy products a day, especially skim milk, and sufficient quantities of lean meat, whole grains, and vegetables. It is also important to monitor patients who take medication that affects the body’s supply of important vitamins and minerals. "Diuretics can wash away dietary magnesium, so we need to watch people on diuretics and consider supplementation if there is no renal insufficiency."
Jorden recommends this menu for a daily supply of magnesium:
1. Breakfast: whole wheat cereal with fruit, milk, or yogurt.
2. Lunch: lean meat sandwich on whole wheat bread, banana, milk.
3. Dinner: tuna, brown rice, carrots, broccoli, milk.
"I think we need to give people the food pyramids and go over it with them, and make meal suggestions," says Jorden.
[Contact Suzanne Humphries at (609) 757-7844 and Jeannette Jorden at (843) 876-1949.]
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