Doctors have long encouraged patients to reduce the amount of saturated fat in their diet. Saturated fat is the predominant fat in meat and dairy foods. The reason? Saturated fat increases LDL-cholesterol, a type of blood fat linked with heart disease. Now a new study shows the type of fat you eat – saturated or polyunsaturated may influence more than just your heart – it may affect your body composition as well.
How Saturated and Polyunsaturated Fats Differ
Saturated and polyunsaturated fatty acids differ in chemical structure. Fatty acids are made up of strings of carbon atoms bonded to hydrogen. Saturated fatty acids have hydrogen bonded to every carbon, making them completely saturated. Polyunsaturated fats have some carbons not bound to hydrogen. Instead, these carbons have double bonds between them. This gives them different characteristics in a laboratory and inside your body. Saturated fats are usually solid at room temperature – think butter and fatty meats, while polyunsaturated fats are usually liquids. Not all saturated fats are animal-based though. Coconut oil, palm oil, and palm kernel oil are high in saturated fat but they’re not derived from animal sources.
Saturated Fat and Body Composition
In a recent study published in the American Diabetes Journal, researchers looked at the impact of saturated and polyunsaturated fats on body composition. They asked 39 healthy, young men and women to eat 750 calories above and beyond their caloric requirements each day for 7 weeks. The goal was to have the participants gain about 3% of their body weight. To meet this objective, one group consumed excess calories from saturated fat in the form of palm oil. The second group got their extra calories from sunflower oil, a polyunsaturated fat.
At the beginning of the study and again at the end, researchers measured the participant’s body fat using an MRI scan. They also looked at gene activity for genes involved in making visceral abdominal fat.
Here’s where it gets interesting. Both groups met their weight gain objective. They all gained weight, but their body compositions were different at the end of the study. The group that ate surplus calories in the form of saturated fat had a greater increase in liver fat and visceral abdominal fat compared to the group that ate polyunsaturated fat. They also put on more total body fat than the group that got their surplus calories from polyunsaturated fat. Visceral fat is the fat that lies deep in the pelvic cavity and accumulates around organs. It’s the most dangerous kind of fat from a health standpoint. Higher levels of visceral fat have been linked with an increased risk for heart disease and type 2 diabetes.
What’s more surprising is how the different types of dietary fat affected lean body mass in the two groups. Participants that consumed polyunsaturated fat gained three times more muscle mass relative to the group that ate saturated fat to achieve their calorie surplus.
By looking at gene activity, the researchers found consuming excess saturated fat activated genes that promote visceral fat storage, increasing the amount of dangerous deep abdominal fat the saturated fat eaters accumulated. At the same time, it turned on genes linked with insulin resistance. More abdominal fat and increased insulin resistance? Not a good thing for your health or body composition.
A Way to Maintain Lean Body Mass?
Researchers point out this study has other implications. As people age, they lose muscle. If this study is confirmed by larger studies, replacing saturated fats with polyunsaturated ones might help people maintain more lean body mass as they age. Of course, resistance training will do this too. Some studies show that omega-3 polyunsaturated fats enhance muscle protein synthesis in response to nutritional factors like protein. Other studies show omega-3 polyunsaturated fats improve bone density too.
This is a small study but it raises interesting questions about how the type of fat you eat influences body composition. Even so, not all polyunsaturated fats are equally healthy. The healthiest ones have a higher ratio of omega-3 fatty acids to omega-6. Omega-6 fatty acids are believed to be pro-inflammatory while omega-3s have anti-inflammatory activity.
All Fats Aren’t Created Equal
Although you need some omega-6 fatty acids to get enough linoleic acid, an omega-6 your body needs but can’t make, most people get too many omega-6s in their diet. That’s because processed foods are usually made with omega-6-rich oils like soybean and corn oil. Other omega-6-rich oils to avoid include safflower oil, cottonseed oil, and peanut oil. Even sunflower oil, the oil used in the study, is high in omega-6s.
In contrast, flaxseed oil and walnut oil are high in omega-3s as is fatty fish like wild-caught salmon. These are “better for you” sources of polyunsaturated fat.
Saturated fats aren’t all necessarily the same from a health standpoint. Research suggests that your body metabolizes tropical oils like coconut oil differently than it does saturated fats from animal and dairy sources. Coconut oil contains lots of medium-chain fatty acids whereas most other fats are made up of long-chain triglycerides. Medium chain fatty acids travel straight to your liver after you eat them where they’re burned off as fuel, much like carbohydrates. In contrast, long-chain fatty acids have to be broken down by your digestive tract and are more likely to be stored as fat. Coconut oil may not have the same negative effects on health as animal-based saturated fats, although more research is needed.
The Bottom Line?
There may be benefits to replacing a significant portion of the saturated fat you now eat with omega-3 rich polyunsaturated fat. One way to do this is to substitute more omega-3-rich fatty fish for the animal protein you’re now eating. Wild-caught salmon, sardines, halibut, and rainbow trout are good choices. Plus, these foods are high in protein and low in calories. Another reason to enjoy more fish!
References:
Medical News Today. “Unsaturated Fat Prevents Abdominal Fat Accumulation Increases Muscle Mass”
Clin Sci (Lond). 2011 September; 121(6): 267-278.
Curr Osteoporos Rep. 2013 Sep;11(3):203-12.
Am J Clin Nutr March 2007 vol. 85 no. 3 803-807.
Rush University Medical Center. “Being Good to Your Heart: Avoiding Holiday Fat”
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