July 2019
CAN EATING FAT MAKE YOU FAT?
Fat vs. Fat: Recent Research suggests that certain types of fat could keep weight off, while others may make you gain. We’ve got the details.
Gone are the days when fat was verboten (thank the avocado gods!) but we also know that not all varieties are created equal. Some, namely monounsaturated and polyunsaturated fats, are more heart-healthy than others (that would be saturated and trans-fats). But recent research is taking that idea a step further: in a first-of-its-kind study, researchers found that certain types of fat are more likely to encourage weight gain, even though all fats have the same calorie count (9 calories per gram).
Frank Hu, MD, chair of the department of nutrition at the Harvard School of Public Health, and his team examined 20-plus years of data from more than 120,000 women and men, looking specifically at how changes in the types of fat that people ate affected their weight. They found that when people increased saturated and trans-fat in their diets, they were more likely to put on pounds. Increasing intake of unsaturated fats had no such connection and was even linked to weight loss. One explanation Hu offers is that different types of fats have different metabolic effects in the body. Saturated and trans fats seem to trigger insulin resistance, meaning that your cells don’t absorb glucose like they’re supposed to. As a result, your body increases its output of insulin, a hormone that promotes fat accumulation. As for unsaturated fats, that’s where it gets interesting. In general, adding more monounsaturated fats (MUFAs) caused a slight increase in weight. However, when the researchers teased out animal sources of MUFAs (like red meat and dairy) versus those from plants (nuts and olive oil), only the animal sources increased weight. Plant sources helped keep the scale steady. This is likely because MUFAs and saturated fats are usually a package deal in animal foods, so you get both good and not-so-good fats. Meanwhile, foods like tuna, salmon, walnuts and sunflower seeds, that are rich in polyunsaturated fats (PUFAs) may prevent weight gain, or help it go down. How? PUFAs appear to promote insulin sensitivity, a good thing for helping the body use food for energy instead of storing it as fat.
Bottom line: Weight gain from eating more trans and saturated fats averaged about ¾ pound per year in the study. This scale creep may not sound like a big deal, but it is enough to increase the risk of diabetes, heart disease and cancer. Hu recommends replacing 5 percent of your saturated fat intake with equal amounts of MUFAs and PUFAs. On a 2,000-calorie diet, if you’re eating 22 grams of saturated fat, you’d just need to cut back by 1.1 grams. That’s like swapping a slice of crumbled bacon on your salad with a generous teaspoon of sliced almonds. And don’t confuse shifting fat with slashing fat. When people reduced the overall fat in their diets, they tend to replace it with refined/concentrated carbohydrates, which may be worse for your health. As long as you focus on quality, there is no need to fear fat.
Source: Science and Nutrition with Eating Well Magazine