Don't blame the food, blame the type of fat we eat. That's what causes us to have big bellies, say Swedish researchers, who used a special muffin diet to demonstrate how this works.

The authors of the study, published last month in the journal Diabetes, say this is the first time research on humans has shown that saturated fat (found in foods like butter, bacon, palm oil and beef) is deposited in a different place on the body than polyunsaturated fat (found in fish, nuts, and olive and sunflower oils).

Saturated fat, they showed, heads straight for the abdomen and liver, where it interferes with our metabolism and increases our risk for diabetes and heart disease. Polyunsaturated fat, on the other hand, gets distributed to other areas of the body, not just the waistline, and is partly used to create  muscle mass.



So how does the special muffin fit in? Researchers randomly divided 39 men and women of normal weight into two groups. They each followed the same diet for seven weeks with one exception: One group ate a 750-calorie muffin each day made with polyunsaturated sunflower oil, while the other group ate the same muffin made with palm oil, which is high in saturated fat and commonly found in packaged foods such as cookies, crackers and microwave popcorn.

Both groups gained comparable amounts of weight, the scientists reported, but magnetic resonance imaging (MRI) scans taken before and after the weight gain showed significant differences between the two sets of participants. The saturated-fat group had "a markedly greater increase in the amount of fat in the liver and abdomen" than the polyunsaturated-fat group. The saturated-fat group also had more total body fat and a much lower increase in muscle mass.

In addition, researchers measured gene activity in the subjects' abdominal fat and found that "over-consumption of saturated fats seems to be able to 'turn on' certain genes in fatty tissue that increase the storage of fat in the abdomen."


So how should you get more foods that fight belly fat in your diet? Here are some tips.
 

• Add avocados. Most of the fat in creamy avocados is poly- and monounsaturated, with an added bonus of some protein. Avocados' healthy fats reduce the sugar spikes that tell your body to add more belly fat. You can include chopped avocado in salads or top tacos with guacamole instead of cheese and sour cream, both high in saturated fat.
• Forget fat-free. Instead of fat-free salad dressing, which has few nutrients and is often overloaded with sugar and salt, opt for a dressing with healthy fats, such as olive oil vinaigrette with vinegar or lemon juice and herbs.
• Bring on the berries. All berries are good for us, but some studies have found that the ketones in raspberries, in particular, prevent fat buildup in the belly and around the liver. Fresh raspberries not in season? Puree frozen raspberries with low-fat Greek yogurt to make a healthy smoothie.
• Nosh on nuts. Snacking on a handful of walnuts or almonds, rich in omega-3 fatty acids, not only reduces hunger pangs, it also fights belly fat, according to a recent Spanish study. All it takes is 1 ounce, equal to a small handful, a day.
• Focus on fish. Fatty fish is an especially good source of important fat-burning omega-3 oils. Twice a week try to have salmon, rainbow trout, arctic char, halibut or albacore tuna.
• Choose alternative oils. Olive, canola, sunflower - sub in more of these polyunsaturated oils for butter and cream. Try these options: Sauté using canola oil, drizzle veggies with seasoned olive oil, and make cream sauces with low-fat plain yogurt.