Does the food we eat affect our body composition? Let's start with the obvious: Caloric surplus makes you gain weight -- too many calories in and too few out and fat accumulates; reverse the equation and weight is shed.
But here's an intriguing question: Can the type of food we eat cause fat to accumulate preferentially in the belly? Do diet choices affect how much muscle we build? It's an important matter, because belly fat isn't just an esthetic issue; fat around abdominal organs behaves like a big endocrine gland, affecting insulin resistance and heart health, while fat elsewhere has fewer health implications.
The fat you eat and the fat you store
A new study in Diabetes, led by Ulf Risérus from Uppsala University in Sweden looked at what overeating saturated fat vs. polyunsaturated fat* does to fat deposits in a neat double blind study experiment.
Thirty-nine adults of normal weight gorged on muffins for seven weeks. They were assigned to eat 750 calories above their normal intake in muffins made with either polyunsaturated fat (sunflower oil), or saturated fat (palm oil). The researchers chose a plant-based saturated fat (rather than butter, for example) in order to avoid confounding cholesterol effects, and because it's a popular ingredient in food industry. Besides the type of fat the muffins had an identical nutrition profile (similar in sugar, protein etc.).
As expected, seven weeks of three extra muffins a day resulted in weight gain -- both groups gained about 1.6 kg or 3.5 pounds.
But the extra fat, measured by MRI scans, was stored in different body locations. The saturated fat group stored twice the amount of fat in the abdomen and had significantly larger stores in the liver. The polyunsaturated fat group spread the extra weight in more favorable ways, and had a nearly three-fold increase in muscle mass. Bottom line: In this small study, saturated fat caused more weight to accumulate as fat, and that fat accumulated preferentially in the liver and around internal organs. While participants gained just as much weight on the polyunsaturated fat muffins, they gained more of it in lean, muscle tissue, and less in metabolically active abdominal fat.
This new study connects saturated fats with preferential belly fat. It is a small study, of short duration, and I'd be curious to see if studies in other populations confirm saturated fat as a fat-belly food.
The food item many people associate with a bulging abdomen is beer, but the beer belly has little scientific support.
Soda belly, on the other hand, might be for real.
A study from the University of California at Davis showed that drinking 25 percent of daily calories (which is quite a lot) in fructose for 10 weeks caused belly fat accumulation -- and increased triglycerides, cholesterol, and insulin resistance.
A recent study found that even moderate consumption of sugary drinks led to measurable undesirable effects after just three weeks: Belly fat accumulated, fasting glucose levels and inflammation markers rose, and the lipid profile changed when volunteers drank what amounted to just one can of soda a day.
Another study in the journal Obesity, following 800 people, found that drinking sugary drinks was associated with significantly more belly fat and wider waistlines.
A study in the American Journal of Clinical Nutrition adds to that body of evidence with a six-month study, in which a small group of overweight people were assigned to drink cola, skim milk, diet cola or water, while fat distribution and metabolic markers were monitored. The total caloric intake didn't differ between the participants, and all the participants gained just about the same amount of weight (almost three pounds). On the other hand, the amount of fat in the liver, abdominal organs and muscle increased significantly in the regular soda group, while it remained unchanged in the other study groups. Blood pressure and triglycerides also rose among the soda drinkers.
A calorie is a calorie when it comes to weight, but not when it comes to health, and these studies suggest that there are indeed foods that make you fat in all the wrong places.
*Most foods contain a combination of fats. Saturated fats are typically solid at room temperature, and include fats that come from animal sources: meat, dairy and poultry, and also from tropical oils such as palm and coconut. Unsaturated fats are liquid at room temperature, and include monounsaturated fats -- olive oil and almonds are rich sources -- and polyunsaturated fats, which are typical of soybean, corn and safflower oil, fatty fish such as salmon, walnuts, and seeds such as flax, hemp and sesame.
Current nutrition understanding is that total fat in the diet isn't the issue; the type of fat and the total calories we consume is. Present-day recommendations: limit saturated fats, eliminate trans fat, and choose foods with monounsaturated and polyunsaturated fats.