Nutriton: An Interview with Dr. Willett
Updated by Dr. Willett, with permission granted to Dr. David Soskin and his organization for clinical use.
Dr. Walter Willett is the Fredrick John Stare Professor of Epidemiology and Nutrition and the Chair of the Department of Nutrition at the Harvard School of Public Health.
How much control do we have over our body weight? And how much of our weight is controlled by our genes?
Dr. Willett: Genes do play a role in controlling our weight, but clearly they do not explain the huge increases in overweight and obesity we have seen in the last 30 years. We gain weight when our "calories in" (the food we eat) exceeds our "calories out" (the energy we burn). Given the genetic package we are born with, we can all improve our weight by paying attention to diet and getting regular physical activity, but some people will need to work harder than others to maintain a healthy weight. In other words, if we all eat and work out the same, we will not all look the same. Only a very small percentage of people have such a strong genetic predisposition that they will be obese no matter how hard they try. Even people who are genetically predisposed to obesity can reduce their risk of chronic disease by eating a healthful diet and staying active.
What is the best diet for losing weight?
Dr. Willett: The real issue is not losing weight-people can cut back on calories and lose weight on almost any diet-but keeping weight off over the long run. Thus it is more important to find a way of eating that you can stay with for the rest of your life. For this reason, any eating plan you choose should be satisfying and allow variety, and should also be nutritionally sound.
The most successful dietary weight control study has been Dr. Iris Shai in Israel with Dr. Meir Stampfer in our department of nutrition. This study compared three diets: a low fat diet, a Mediterranean Diet, and a healthy higher fat diet. After 18 months the low fat diet was the least effective. Most importantly, after six years, weight loss was maintained best with the Mediterranean diet, and blood indicators of metabolic status were also superior.
If you are interested in following this type of eating plan, I suggest using the Harvard School of Public Health's Healthy Eating Pyramid and Healthy Eating Plate as a guide. Like the Mediterranean diet used in the weight loss study, the Healthy Eating Pyramid emphasizes fruits, vegetables, whole grains, nuts and legumes, healthy oils, and daily physical activity. To lose weight, watch your portion sizes and aim for a modest reduction in your daily calorie intake. My recent book with Mollie Katzen, Eat, Drink and Weigh Less (Hyperion, 2006), follows the same nutritional principles as the Healthy Eating Pyramid and details many eating strategies for weight control.
The Nine Turning Points
Following these diet and lifestyle guidelines can help you achieve a healthy weight and reduce your chronic disease risk:
1. Eat lots of vegetables and fruits.
2. Say yes to good fats.
3. Upgrade your carbohydrates.
4. Choose healthy proteins.
5. Stay hydrated.
6. Drink alcohol in moderation (optional).
7. Take a multivitamin every day.
8. Move more.
9. Eat mindfully all day long.
Source: Katzen M, Willett WC. Eat, Drink and Weigh Less: A Flexible and Delicious Way to Shrink Your Waist Without Going Hungry. New York: Hyperion; 2006. p.14-15.
Can I lose weight through diet alone? Or do I need to exercise, too?
Dr. Willett: Daily physical activity can help you control your weight and can reduce your risk of chronic disease. That's why it is the foundation of the Harvard School of Public Health's Healthy Eating Pyramid. Aim for at least 30 minutes a day of physical activity; many people will find that 60 minutes a day is helpful for weight control. For more information on the benefits of physical activity, read the article about staying active.
Will going on a low-carbohydrate diet help me lose weight?
Dr. Willett: Some people who go on a low carbohydrate diet have managed to keep weight off, but the best studies show that on average the weight loss is small after one year. There has been much debate about the impact of low carbohydrate diets on overall health. Our recent 20-year study on 82,080 women found that that a low carbohydrate eating pattern did not increase risk of heart disease; if the protein and fats mainly came from vegetable sources, a low carbohydrate eating pattern actually reduced heart disease.
Should I cut back on fat to lose weight?
The goal is to cut back on calories, and a common mistake is to focus only on fat. Fat is satisfying, and in the long run low fat diets have generally failed as a way of weight control. For good health, the type of fat is more important than the amount; eat plenty of unsaturated fats, limit saturated fat, and avoid trans fat. For more information on how to choose healthy fats, read the article about Fats & Cholesterol.
What are the best fruits and vegetables to eat if I want to lose weight? Which fruits and vegetables should be avoided?
Dr. Willett: Chose a wide variety of vegetables and fruits every day, but don't include white potatoes as a vegetable. Potatoes are a starch, and a rapidly-digested one at that; nutritionally, they have more in common with white bread and white rice than with other vegetables, and they should be eaten only occasionally. Go easy on fruits that are higher in carbohydrate, such as oranges, bananas, apricots, cherries, grapes, mangoes, pineapple and pears. Also, avoid fruit juices, since they contain a lot of sugary calories; choose whole fruit instead, since it has more fiber and will make you feel more full.
Which type of protein is best for me to eat-vegetable protein or animal protein?
Dr. Willett: Emphasizing vegetable over animal sources of protein will help reduce risk of heart disease. For example, this means eating nuts, beans, and soy products instead of red meat, which contains a lot of saturated fat and cholesterol. However, a healthy diet can include moderate amounts of poultry, fish, and eggs.
Will drinking milk or eating yogurt help me lose weight?
Dr. Willett: Long term studies do not show a benefit of milk for weight loss, which should be no surprise as even low fat versions still contain quite a few calories. Recent studies do suggest that men and women who consume yogurt regularly have less long term weight gain, but more research is needed.
Every month, I read about a new type of diet that promises to help me lose weight fast. How can I tell if a diet is safe and effective?
Rigid diets usually fail in the long run. I would be wary of any diet that eliminates entire food groups or drastically reduces one food component (such as diet that is very low in carbohydrates). Diets that recommend skipping meals or replacing meals with special supplements are also suspect.
Will supplements such as conjugated linoleic acid, omega 3 fish oil, or vitamin B6 help me lose weight?
Dr. Willett: None of these supplements have been shown to reduce weight. A multiple vitamin is a good nutritional safety net for most people, and for premenopausal women it is good to use a preparation that includes iron.
How can I find out how much I should weigh?
There is no single number that works for everyone. Your body-mass index, or BMI, a ratio of weight to height, is one way to tell if you are at a healthy weight (you can calculate your BMI online). Almost everyone should try to keep their BMI below 25. Also, keep in mind that most of the weight we gain in adulthood is fat. So unless you were clearly underweight at age 18 or 20, it is best not to gain more than 5 or 6 pounds after this age. For someone who is very overweight, it is usually not realistic to go all the way back to your weight at age 18; even a 5 to 10 percent weight loss has important health benefits.
How often should I weigh myself?
Dr. Willett: Once a week is a good interval. It is also a good idea to keep an eye on your waist circumference; even an inch or two increase in waist size is a sign that you may need to cut back or calories, exercise more, or both."
For more information on diet and nutrition go to Dr. Willet's website: http://www.hsph.harvard.edu/nutritionsource/weight-control/
Eat, Drink, and Be Healthy: The Harvard Medical School Guide to Healthy Eating by P.J. Skerrett (Afterword, Contributor), Walter Willett M. D. (Author)
Weight loss: Eat, Drink, and Weigh Less: A Flexible and Delicious Way to Shrink Your Waist Without Going Hungry Paperback by Mollie Katzen (Author), Walter Willett (Author)