Harley Pasternak is a celebrity trainer and nutrition expert who has worked with stars from Halle Berry and Lady Gaga to Robert Pattinson and Robert Downey Jr. He’s also a New York Times best-selling author, with titles including The Body Reset Diet and The 5-Factor Diet. His new book 5 Pounds is out now. Tweet him @harleypasternak.
Research on health and nutrition is ongoing, as is the case in any field. In science, the “truth,” if that is even a correct term, is a constantly moving target. Based on a recently published study by researchers at the University of California-Riverside, it may well be time to overthrow some conventional wisdom about the causes of obesity and type 2 diabetes.
Studies on heart disease published half-century ago linked saturated fat to cardiovascular disease, which has been the bad boy of the fat world ever since. But the results of this new study, which used mice as subjects, suggest that at least one saturated fat is less likely than at least one unsaturated fat to be associated with obesity and diabetes. Another nutritional “truth” is that over-consumption of fructose, a type of sugar, is a major player in causing both obesity and diabetes. However, this recent research also suggests that a diet high in the same unsaturated fat may be more likely to result in both health problems than is a high-fructose diet.
Fast Facts on Fats
Let’s lay some groundwork before looking more closely at the study. There are three forms of natural fats: monounsaturated, polyunsaturated and saturated. Generally, olive oil and other (primarily) monounsaturated fats (MUFAs) such as canola, walnut and other nut oils, as well as avocados, are considered desirable. So are polyunsaturated fats (PUFAs), which include corn, sunflower, safflower, soybean and grapeseed oils, as well as some nuts, seeds and fatty fish. Both MUFAs and PUFAs are liquid at room temperature. Saturated fats, such as butter, palm oil, coconut oil, beef suet and other animal fats are solid at room temperature.
For decades, we’ve been told to limit our intake of saturated fats for health reasons. In the most simplistic terms, MUFAs and PUFAs have been considered “good” and saturated fats were considered “bad.” (The even worse guys are trans fats, a.k.a. partially hydrogenated oils, which have a been blasted with hydrogen gas to make them more stable and thus extend shelf life.)
Same Calories, Different Diets
The researchers divided the mice into four groups. On average, Americans eat a diet that is comprised of 40 percent fat; so all four groups of mice received a diet with that same percentage. The calorie count of all four diets was also identical; however, two of the groups of mice received additional fructose, comparable to the amount that Americans consume on average each day. The four diets:
· Diet No. 1: enriched with coconut oil (primarily a saturated fat)
· Diet No. 2: enriched with soybean oil (primarily a PUFA)
· Diet No. 3: enriched with soybean oil and added fructose
· Diet No. 4 enriched with coconut oil and added fructose
Coconut Oil Beats Soybean Oil
When the mice on the first two diets were compared at the end of the study period, those who had consumed soybean oil (group one) had gained almost 25 percent more weight than group two. They also put on more fat and were more likely to have a fatty liver, diabetes and insulin resistance than the mice whose source of fat was coconut oil. These factors are all indicators of metabolic syndrome, which is often a precursor to type 2 diabetes.
The mice that were given added fructose showed more kidney problems and symptoms of inflammatory bowel disease (IBD), but not the differences in weight and other metabolic factors found between the soybean oil and coconut oil diets. The mice on Diet No. 3 also gained 9 percent more weight than the mice on Diet No. 1, which were getting coconut oil but no added fructose.
What Does It All Mean?
The researchers acknowledged that they were surprised by the results. Conventional wisdom is that over-consuming sugar in all its forms, including fructose, is the culprit when it comes to obesity and diabetes. Until now, soybean oil has never been linked to either condition. But we now consume far more soybean oil than we did 50 years ago. It’s found in most processed food, including everything from potato chips and packaged cake mixes to bottled salad dressings and microwaveable entrées. Soybean oil is often the main component of so-called “vegetable oil,” too.
A Case of Unintended Consequences?
While still preliminary, this research suggests that one of the several ways in which most people in Western societies eat today is likely a major factor in the current epidemic of weight gain, obesity and diabetes. Once those 50-year-old studies implicated saturated fat as a factor in heart disease, government guidelines encouraged Americans to cut back on those fats found in meat and dairy and to replace them with plant oils, including soybean oil. (There has also been an increase of about 33 percent in the intake of fructose in the same time period.)
Today, 60 percent of oil in the food supply comes from soybeans. And its increase in consumption is equivalent to the rise in obesity over the last four decades. The same researchers also studied corn oil, and found it more likely to lead to obesity than coconut oil, but less so than soybean oil. Tests on lard and olive oil are currently underway.
As the researchers pointed out in their conclusions, not all saturated fats are alike in their chemical composition. Likewise, not all PUFAs or MUFAs are alike. It’s worth reiterating that the original studies done on saturated fats included animal fats, not coconut oil.
5 Action Steps
In general, it is never good to eat too much of a single food. In regards to this study, understand that it’s just one case and there is no way to know if people will respond as mice did to the different diets. Nonetheless you might want to make some changes to your eating habits to minimize your intake of soybean oil:
1. Moderate your intake of all soy products, including soybean oil. Soy also contains plant estrogens, which is another reasons not to overeat such products.
2. Make your own salad dressings, using olive oil and vinegar or lemon juice. Most manufactured salad dressings contain soybean oil or “vegetable” oil.
3. Read food labels to check whether fructose or soybean or “vegetable” oil is one of the primary ingredients.
4. Use olive oil in marinades or basting sauces for broiling or grilling meat, poultry, fish or vegetables.
5. Experiment with coconut oil in baked goods or for sautéing. Some find the taste off-putting; others are pleased by the results.
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