Nutrition Archive

Various herbs and other supplements have been touted for their ability to improve cholesterol levels. Here's what the research shows — and doesn't show — about some of the best-known products.

Hawthorne. The leaves, berries, and flowers of this plant are used to make medicine that was traditionally used to treat cardiovascular diseases. It may lower cholesterol by increasing the excretion of bile and decreasing the body's production of cholesterol. Verdict: It may possibly help.

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Think about this the next time you fill your plate with kale or spinach: a study published in JAMA Ophthalmology Jan. 14, 2016, found that boosting leafy green vegetable intake is associated with a reduced risk of developing glaucoma, a leading cause of blindness.

Harvard researchers analyzed the dietary information reported by more than 100,000 men and women in two long-term studies, each lasting more than 25 years. Those who ate the most leafy greens had a risk of developing glaucoma that was 20% to 30% lower than that of those who ate the least. What's the link? Glaucoma causes damage to the optic nerve, through increased pressure from fluid in the eye or impaired blood flow to the optic nerve. Leafy greens are loaded with nitrate, which the body converts to nitric oxide. "Nitric oxide is important for maintaining optimal blood flow, and possibly for keeping eye pressure low," speculates Dr. Jae Hee Kang, the lead author of the study and a Harvard Medical School assistant professor. The study doesn't prove that leafy greens reduce glaucoma risk; it only shows an association between the two. Eating leafy greens is also linked to lower rates of inflammation, cancer, heart disease, and even macular degeneration.

When it comes to preventing cardiovascular disease, some experts feel the recommendations may not go far enough.

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Every five years, the U.S. government issues a new edition of the Dietary Guidelines for Americans, a report that "helps Americans make healthy choices for themselves and their families." But if you're concerned about having a heart attack or stroke, the advice in the latest update doesn't entirely agree with what many nutrition experts—as well as the American Heart Association—recommend.

We asked Dr. Walter Willett, professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health, to share his thoughts about where the new guidelines may not be aggressive enough for people at risk for heart disease. Here's his advice on five dietary components of note.

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The popular eating pattern that's good for your heart—the Mediterranean diet—is also good for your waistline, according to a review of five studies that compared the Mediterranean diet with other weight-loss diets.

The trials, which included a total of 998 overweight or obese people, pitted the Mediterranean diet (which is rich in vegetables, fruits, grains, beans, and olive oil but light on meat, dairy, and eggs) against one or more of three other diets: a low-fat diet, a low-carb diet, and the American Diabetes Association (ADA) diet.

Drinking caffeinated coffee or tea may help you feel more awake and alert. But for healthy people, it probably won't cause palpitations—a noticeably strong, fast, or irregular heart beat. That's according to a new study of nearly 1,400 older adults in the Jan. 26, 2016, Journal of the American Heart Association.

Researchers relied on data from food questionnaires and Holter monitors, which recorded each participant's heart rhythm for a 24-hour period. About 60% of the people in the study said they consumed more than one caffeinated product (coffee, tea, or chocolate) a day. People who consumed more of those products were no more likely to have palpitations than those who imbibed less, the authors found.

The USDA recently updated its recommendations for healthy eating. Here are the takeaway messages for men.

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Every five years, the USDA releases its Dietary Guidelines for Americans—advice to encourage healthier eating patterns based on the latest nutritional science.

"While there is a lot of nutritional information out there, the guidelines are the foundation for many government food programs, and many men can benefit from their recommendations," says Katherine McManus, director of the Department of Nutrition at Harvard-affiliated Brigham and Women's Hospital.

Ask the doctor

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Q: My doctor advised me to give up my soda habit, but I was thinking about switching to diet soda. What is your advice about the safety of artificial sweeteners?

A: I support your decision to decrease the amount of added sugar in your diet, but it is less clear if artificial sweeteners are the answer. These sugar substitutes do appear to be safe when consumed in usual amounts. Initial studies in rats, performed decades ago, raised a possible link to bladder cancer, but no subsequent studies in humans have confirmed this relationship.

Vitamin D supplementation has been proposed as a possible preventive strategy to improve lower-extremity function and reduce risk of falls among older adults. But taking higher doses does not improve function and also may increase the risk of falls, according to a study in the February 2016 issue of JAMA Internal Medicine.

The recommended daily allowance is 600 international units (IU) for men ages 51 to 70 and 800 IU for those older than 70. Many older adults get too little vitamin D in their diet and from sun exposure.

The final recommendations do not specify limiting consumption of red and processed meats, which have been linked to cancer risk.

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The report of the Dietary Guidelines Advisory Committee, released in February 2015, suggested that the then-forthcoming update to the Dietary Guidelines for Americans adopt several changes from previous versions. It advised limiting added sugars to 10% of calories; removing the ceiling on dietary fats as long as saturated fat comprises no more than 10% of calories; and limiting consumption of red and processed meat.

When the final guidelines were released by the Department of Health and Human Services (HHS) and the Department of Agriculture (USDA) in January 2016, the caveat on red and processed meat was missing. Through that omission, the guidelines "censored conclusions of the scientific advisory committee," according to a statement on the website of the Harvard T.H. Chan School of Public Health. Dr. Frank Hu, Harvard professor of nutrition and epidemiology, was a member of the federal Dietary Guidelines Advisory Committee, which spent two years reviewing reams of scientific evidence on diet and health and drafting the guidelines that were submitted to HHS and USDA. "Although there are some areas of improvement in this edition over previous ones, some simple but important recommendations are watered down, especially reducing consumption of red and processed meat," he says.