Low-Fat Diets Are Not The Solution To The Obesity Epidemic
Professor Walter Willett is Professor of Nutrition at the Harvard School of Public Health (Boston, Massachusetts) and is considered one of the best, if not the best, nutritionist in the world. In this interview he specifies some of the data on nutritional factors related to diabetes and obesity.
Professor Walter Willett, the chair of the Nutrition Department at the Harvard School of Public Health (Boston, Massachusetts), is considered one of the best, if not the best, nutritionist in the world. At his side is working the team of the most prestigious epidemiologists in this field. For nearly 20 years, they have followed two enormous cohorts: the 80,000 women in the Nurses ‘Health Study and the 50,000 men in the Health Professionals’ Follow-up Study ). The information accumulated by Walter Willett and his team from these unprecedented prospective studies has provided valuable insight into the health impact of diet. These data are published in the leading medical journals. They inspired many chapters of “Health, lies and propaganda”, the book by Thierry Souccar and Isabelle Robard, and “Milk, lies and propaganda”, to which Professor Willett gave his support. In this interview, Professor Willett outlined some of the most recent data on nutritional factors related to diabetes and obesity.
What can be attributed to the obesity epidemic affecting Western countries?
There are many factors contributing to this, but all of them are either reduced physical activity or increased calories. Unfortunately, our society encourages inactivity; School physical activity programs are all too often reduced or eliminated. The number of hours spent watching television is enormous, and in many studies it is the most strongly associated with being overweight. Of course, the agri-food industry has its share of responsibility. She leads extensive research programs to find out how to make us eat more, for example by maximizing convenience, playing on color, sugars, calories. In other words, it creates hooks to exploit human weaknesses and we bite into it. Unfortunately, the scientific community has contributed to this problem by conveying the message that only fat calories count, and this has led to a great deal of belief that large quantities of sugar, cereals, Pay the price in terms of weight.
Many people, however, try their doctor’s advice to lose weight by eating less fat.
I have just published a synthesis of studies on the relationship between dietary fat and body weight. It is true that some, when prescribed a diet low in fat, will lose a few pounds in a few months. But most of them return before a year. Considering studies of this type that lasted more than one year, they showed no appreciable reduction in body weight. One of the best controlled studies was reported by Dr Sacks and McManus: after 18 months, people on a low-fat diet actually lost less weight than those on a Mediterranean-type diet with an intake of Fats moderate. (1) Thus, there is now strong evidence that low-fat diets will not be the solution to the obesity epidemic.
For many nutritionists, carbohydrates have no impact on waist circumference.
There is a widespread belief among the public and some doctors that it would be impossible to grow by consuming carbohydrates. It’s silly ! You can grow with an excess of calories, no matter where it comes from. The explosion of obesity in developed countries may be due to this belief that carbohydrates do not make you fat! We have studies that suggest that refined carbohydrates disrupt the appetite control mechanisms. After a meal rich in fast carbohydrates, one feels full at first. The blood sugar rises, but under the influx of insulin, it then goes down too low, and we need to feed again. This is one of the mechanisms by which fast carbohydrates maintain hunger. It is very possible that, depending on whether fast or slow carbohydrates are used, weight gain is favored or not.
Do the current nutritional recommendations take these differences into account?
We have a dietary “pyramid” in the United States to visualize the relative share of each food group in an ideal diet. This pyramid is not even worth the paper on which it is printed. The message we get is that carbohydrates are good, and bad fats. This is not correct. By following such recommendations, one can increase his cardiovascular risk, by abandoning good fats and overloading carbohydrates. The problem is that the scientific community has the greatest difficulty in questioning itself.
You publish nutritional recommendations that rehabilitate fats since they occupy a place as important as carbohydrates. Are not fats harmful to health?
There has never been any serious evidence that the share of calories brought by fat plays a large role in long-term health. That’s why I put the “good” fats next to the “good” carbohydrates in my recommendations.
Many doctors and nutritionists believe that consuming carbohydrates does not increase the risk of diabetes. What did you find on your side?
We’ve known for a long time that very refined carbohydrates are causing blood glucose levels to rise dramatically and trigger insulin excretion. We have therefore hypothesized that people who consume too much refined foods have a chronic excess of insulin that can deplete the pancreas and lead to diabetes. We have shown that women who diet high in fast carbohydrates and low in fiber have a risk of diabetes multiplied by 2.5. In men, the risk is similar.
What is at issue is white sugar?
Not particularly. We looked at foods that have a high glycemic index, that is, to schematize, those that have a significant impact on blood glucose. The white sugar is half glucose, which has by definition a high GI, and half fructose, which has a low GI. White sugar therefore has an average GI. The white bread baguette, fried potatoes, some breakfast cereals have a higher glycemic index.
Does diabetes appear only in genetically predisposed individuals?
No. The main factors are diet and lifestyle. A major risk factor is excess body fat, which is related in particular to the level of physical activity.
Do refined carbohydrates have other health consequences?
We found an association between diets high in carbohydrates with high glycemic index and the risk of cardiovascular disease in women. Those who consume the most of these carbohydrates have a risk multiplied by 2. One thing seems clear, the adverse effects of a diet high in refined carbohydrates depend on individual resistance to insulin, that is to say l Ability of cells to capture blood sugar. Jefferson’s study of US Post employees showed that diets high in refined carbohydrates increase insulin levels and triglycerides especially as insulin resistance is pronounced.
What advice can you give to stay healthy?
It is important to stay slim and active, engage in regular physical activity such as walking. Saturated fats and “trans” fats should be replaced whenever polyunsaturated fats are used as vegetable oils. Consume low-processed, low-refined, high-fiber carbohydrates. Potatoes should be eaten in moderation: this food is not suitable for a sedentary lifestyle. You have to alternate red meat and white meat. The first is not good when it is consumed on a daily basis. The fish appears protective. Simple sugars should be used sparingly: they tend to replace healthier foods and can contribute to the glycemic load. Carbohydrates with high glycemic index are only really problematic for sedentary individuals.
(1) McManus K: A randomized controlled trial of a moderate-fat, low-energy diet compared with a low fat, low-energy diet for weight loss in overweight adults. Int J Obes Relat Metab Dis 2001, 25 (10: 1503-1511.