So, you’ve put on some pounds over the past few years and your doctor told you to drop some weight by “eating better.” What exactly does that mean? You have probably been told somewhere along the line that fat is bad, meat is bad, milk and cheese and eggs are bad, sugar is bad, bread and pasta and rice are bad, gravy and sauce are bad, butter and ice cream are bad, soda is bad, snacks and desserts are bad, junk food is bad and salt is bad. What does that leave except cardboard and vitamin pills? How come people ate without worry and without getting fat 50 years ago?
Americans have been told by government nutritional experts to eat a low-fat diet for about 3 decades, during which time America has tripled its obesity rate. But everyone knows eating fat makes you fat, right? Perhaps your doctor, or dietician or a magazine article told you it really doesn’t matter what you eat, it’s as simple as “calories in and calories out” and that fat has tons of calories so don’t eat it… but it feels like you don’t eat very much already! And when you try to eat just that salad for lunch, you get so hungry you can’t think straight or take the time to make a good dinner. So, what’s the right answer? Why is America getting so fat so fast despite trying so hard?
Sometimes scientists take information and extrapolate (guess!) too much. For example, FAT is indeed 9 Calories per gram as opposed to 4 calories in a gram of PROTEIN or CARBOHYDRATE. (All food, except for alcohol, is made up of water plus the three types of NUTRIENTS, which are fat, protein and carbohydrates.) It’s also true that rats fed high fat rat chow get fat unless the amount of chow is decreased to compensate for the extra calories. However, people who try to eat low fat diets don’t necessarily gain less weight than people who eat higher fat diets. Since you are not a rodent in a cage in a lab, let’s take a look at what happens to real people in real life.
Believe it or not, doctors and nurses get the same health issues as most other Americans and are willing to fill out surveys and get blood tests and exams so that we can get some answers about health outcomes over time. There are two large studies of nurses followed 12 to 20 years. These are the Nurses’ Health Study (NHS), and the Nurses’ Health Study 2 (NHS 2). There is also one of doctors followed 20 years, called the Health Professionals Follow up Study (HPFS). These people may not properly represent the ethnic and financial diversity of our nation, but information based on 20 years of follow up in over 120 thousand people is still worth looking at. A recent evaluation of data from these studies with regard to diet and weight gain was published in the New England Journal of Medicine (1) and sheds some light on what works and what doesn’t.
So which is it, quantity of food or the quality and types of food that causes the weight gain? Well, the answer is that both matter, but you might be surprised by which foods are associated with weight gain, (and heart disease and diabetes), and which are not. First let’s talk about why this analysis means something. This paper used data from the three studies listed above (NHS, NHS2, HPFS) which were prospective cohort studies. That means all the data was collected as the years went on, not recalled at the end, and that the outcomes of people who did or did not eat or do something were compared. Proven statistical methods were used to account for different weight outcomes due to factors other than types of food, such as starting age, starting weight, physical activity, smoking, alcohol use, TV watching time and sleep hours. People who were already obese or were over the age of 65 at the start of the study were excluded, so this paper relates more to people who have gained weight in adulthood. The statistical association is strong (likely to be real) and dose dependent, meaning that the people who ate most of the bad foods and least of the good foods gained the most weight. While this does not prove that the food types caused the weight gain, it’s probably more important than what happens to rats in a lab. I should also mention that the average weight gain for this population was 0.8 lbs a year, so most people gained weight over time, but some gained more (or a lot more) than others.
In contrast to milk, there have been a number of human and animal studies showing that consumption of fructose and sucrose (soda and sugary drinks) increases serum uric acid, which in turn increases blood pressure and also causes gout. Confirming this, there was also a recently published study of about 3000 people in the US and UK which showed higher blood pressures in people who consumed more sugar-sweetened beverages (2), and another recent study of data from that same Nurse’s Health Study (NHS) we’ve been discussing, which showed an increased incidence of gout in women who drank more sugar-sweetened beverages. So the most important food to give up is those sugary beverages.
Overall, it’s clear that Nuts and Dairy foods are not the terrible fattening things we thought (plus dairy foods provide important calcium), and that potatoes, sugary beverages, refined grains and excess meat are likely to cause weight gain.