Eating a low fat diet has long been thought to help reduce our risk of developing these life-threatening diseases—and perhaps over the long term it does, if we start from a relatively young age, and in conjunction with other lifestyle changes. But in this eight-year study of 48,835 women, with an average age of 62, the results showed no difference in the rates of these diseases between those on the low fat diet and those on a regular diet. Moreover, the women on the low fat diet ate more whole grains, fruits and vegetables, yet these did not make any difference.
What can we infer about low fat diets?
First of all, low fat diets won't work in a vacuum. Following a low fat diet is part of a healthy living equation that includes:
- Keeping overall fat intake between 20% and 30% of daily calories
- Choosing good fats over bad (unsaturated fats in salmon, nuts, seeds, olive oil over saturated fats or trans fats found in red meats, full-fat dairy, processed foods and fast food)
- Eating more fruits, vegetables, legumes and whole grains
- Cutting refined carbohydrates (the white stuff!)
- Limiting sodium intake
- Practicing portion control
- Increasing physical activity
- Staying hydrated
So back to the study itself: was it flawed?
- By focusing on one particular sub-group of the population—overweight, post-menopausal women—we can’t be certain that the results would have been replicated across the general population.
- An eight-year study is indeed a long one, but to see the kind of results we would hope for, a broader sample of the population would need to be studied over an even longer period, say 15-20 years.
- Some, including Dean Ornish, a well-known low fat guru, argue that the low fat goals weren't strictly adhered to. The intention was to have the women on a low fat diet eat just 20% of calories from fat. But in reality they started by eating 24% of calories from fat, creeping up to 29% later on. True, this hardly seems excessive, but if the object was to see what staying at 20% would yield, then we failed to see the effect.
- The women on the low fat diet were counseled to reduce fat, period, rather than to limit fat intake to the “right” kinds of fats. In recent years we have been advised to make a distinction between the good fats and the bad fats. Swearing off nuts but picking at potato chips would be an example of a bad choice. Eating salmon rather than steak would be a good choice. Would the outcome of the low fat study have been different if the women had been told to choose unsaturated fats, and to avoid saturated and trans fats?
- It’s unclear whether the women in the study were limiting their portions, or raising their level of physical activity to any significant degree during the study.
Some encouraging trends that emerged from the study, which some of the media ignored or glossed over, came from the group that started with the highest intake of fat and reduced it the most. These women cut their risk of breast cancer by 15-20%. The other women on the low fat diet reduced their risk by a less significant 9%—still a worthwhile reduction. The women on the low fat diet reduced their LDL (bad) cholesterol slightly; and those who cut their intake of saturated fat and trans fats the most while increasing their intake of fruits and vegetables, had better results than their peers.
The best we can do is live and eat as healthily as possible. With two-thirds of the US population either overweight or obese, we're clearly not doing that right now. Until we know more from studying a broader range of the population, while focusing on certain kinds of fats, there’s no good reason to abandon a low fat diet. For many, a low fat diet, combined with the other parts of the healthy living equation, helps people control their weight—which in itself may ward off life-threatening diseases.
