News Review From Harvard Medical School -- Stronger Evidence Favors Mediterranean Diet
A new study may provide the best evidence yet that a Mediterranean-style diet reduces people's risk of heart attack and stroke. Unlike previous studies, the new one randomly assigned 7,500 people to specific diets. They followed the diets for 5 years. In that time, people on Mediterranean diets had a 30% lower combined rate of heart attack, stroke and deaths from related causes. Considered separately, only the stroke rate reduction was large enough to be clearly not the result of chance. Everyone in the study had a high risk of developing heart disease or stroke. Nearly all were overweight or obese. Most had high blood pressure and high cholesterol. About half had diabetes. Two groups were randomly assigned to a Mediterranean diet. This included lots of fruits, vegetables, whole grains, tomato sauce, fish and legumes. One group also consumed about 4 tablespoons of olive oil each day. The other ate a handful of nuts daily. The third group followed a low-fat, high-carbohydrate diet. Researchers did urine and blood tests to ensure people followed the diets. The New England Journal of Medicine published the study online. The Associated Press wrote about if February 25.
By Howard LeWine, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
A Mediterranean eating pattern was first described in the 1950s. It was part of a study of health and habits in seven countries: Greece, Finland, Italy, Japan, the Netherlands, the United States and Yugoslavia. The researchers were surprised to find that people living in Greece and southern Italy lived the longest. They did this in spite of a high-fat diet and limited medical care.
The person who started the study 60 years ago was the nutrition expert Ancel Keys. When he turned 100, he was asked whether his diet might have contributed to his long life. His answer: "Very likely but no proof." Keys died in late 2004, about 10 months after reaching the century mark.
Keys' answer was right on target. There have been plenty of studies showing a strong link between eating a Mediterranean-type diet and fewer heart attacks and strokes. And clearly this type of diet helps lower cholesterol levels and blood pressure. But that's not proof of longer life.
These studies were all observational. They compared what happened to groups of people who were similar except for what they usually ate. Until now, no clinical trial has clearly shown that eating a Mediterranean-style diet reduces your risk of heart attack, stroke or death from related diseases. A clinical trial randomly assigns people who are otherwise similar to follow different behaviors or treatments. Clinical trials provide the best chance of showing a true cause and effect.
The people chosen for this study were the ones most likely to see health benefits from a Mediterranean-style diet. Most of them had at least one major factor that increased their risk of heart attack and stroke.
They included people with large waists, diabetes, high blood pressure and high cholesterol. In this study, more than 80% had high blood pressure. More than 70% had abnormal cholesterol levels and 50% had diabetes. The average waist size was well over what is considered abnormal.
The researchers compared the Mediterranean style of diet to a typical high-carbohydrate, low-fat diet. Compared with the other diet, the Mediterranean-style diet reduced the risk of heart attack, stroke and death from these types of diseases by 30% over 5 years. Does a Mediterranean-type diet extend life for those at low to average risk of heart disease and stroke? There's still no definite answer to that question. Again, based on prior observational studies, this type of diet appears to be linked with a lower risk of dying from any cause.
What Changes Can I Make Now?
There is no specific Mediterranean diet. Based on this study and many others before it, here are the main components of a Mediterranean style of eating:
- Four or more servings of vegetables a day. A serving is ½ cup of raw or cooked vegetables, 1 cup of raw leafy greens or ½ cup of vegetable juice.
- Four or more servings of fruit a day. A serving is ½ cup of fresh, frozen or canned fruit; ¼ cup of dried fruit; one medium-sized piece of fruit; or ½ cup of fruit juice.
- At least 4 tablespoons of olive oil a day.
- One handful (about 1½ ounces) of nuts, 3 or more times per week.
- Three or more servings of legumes (beans, peas and lentils) per week. A serving is ½ cup.
- Six or more servings of whole grains a day. A serving is 1 cup of dry breakfast cereal; ½ cup of cooked cereal, brown rice or whole-grain pasta; or one slice of whole-grain or multi-grain bread.
- Three or more servings of fish (especially fatty fish) a week. A serving is 4 ounces.
- One serving of yogurt or cheese a day.
- If you enjoy alcohol, limit yourself to 1 (for women) or 2 (for men) drinks a day. One drink is 5 ounces of wine, 12 ounces of beer or 1½ ounces of liquor.
- Soda and sugary drinks
- Sweets, pastries and commercial bakery goods
- Red and processed meats (eat white meats instead)
- Margarines and most tub spreads
You also have a good chance to lose some weight with a Mediterranean-style diet. But you still need to pay attention to your total calories.
What Can I Expect Looking to the Future?
Most diet advice today has already moved toward a Mediterranean style of eating. You can expect that trend to continue.
This particular study suggests that olive oil and nuts may have special health benefits. They are both high in calories. As with many things in life, the message once again is moderation.