A calorie is a calorie – or is it? Not according to a recent study. This study looked at three different diets – a low-carbohydrate diet, a low-glycemic diet, and a low-fat diet. According to this study published in the Journal of the Medical American Association, each of these diets has metabolic benefits and drawbacks.
How the Type of Calories You Eat Affects Energy Expenditure
Researchers at the Obesity Prevention Center at Children’s Hospital in Boston looked at the effects of these three diets on energy expenditure and metabolism. One group of men and women were assigned to a very low-carbohydrate diet that consisted of 10% carbs, 60% fat and 30% protein. Another group ate a low-fat diet (20% fat, 60% carbohydrate, 20% protein), while a third group ate a low-glycemic diet, emphasizing unprocessed foods that are low on the glycemic scale. At the end of four weeks, the participants switched diets so that they ate each diet for 4 weeks and consumed an identical number of calories during each 4-week period
The results? The participants who ate the low-fat diet had a lower resting energy expenditure compared to those who ate the low-carb and low-glycemic diet despite eating an equivalent number of calories. On the other hand, the low-carb dieters experienced the greatest metabolic boost. They burned an additional 350 calories per day compared to the low-fat dieters.
The low-glycemic diet also boosted resting energy expenditure relative to the low-fat diet, although not as much as the low-carb diet. On the low-glycemic diet, the participants burned an additional 150 calories a day.
Downsides of the Low-Carb Diet
Even though the low-carb diet boosted energy expenditure the most, it wasn’t the healthiest option. Participants on the low-carb diet had higher levels of the stress hormone cortisol and an increased level of an inflammatory marker called c-reactive protein or CRP. This suggests that the low-carb diet placed more stress on the body and may increase the risk of heart disease since higher levels of CRP are a marker for a greater risk of heart disease.
On the other hand, the low-fat diet had drawbacks too. Not only did it not increase resting energy expenditure, but it also increased insulin resistance and triglyceride levels while lowering levels of HDL, the “good” form of cholesterol that protects against heart disease. Both the low-carb and the low-fat diets appeared to be less heart-healthy in this study than the low-glycemic diet.
What Does This Mean?
Diets that greatly limit one dietary component while emphasizing another aren’t the healthiest choice. Even though a low-carb diet burns more total calories, it also places more stress on your body and may increase your risk for heart disease. Consistent with this, a recent study found a link between low-carb diets and a greater heart disease risk. On the other hand, low-fat diets don’t appear to be heart healthy either, and they don’t give you the extra metabolic boost that a low-carb diet that’s higher in protein does.
The best choice appears to be a low-glycemic diet that emphasizes healthy, fiber-rich carbs, moderate amounts of protein and fat and de-emphasizes processed foods. In the study, this type of diet modestly boosted total energy expenditure and wasn’t associated with increased inflammation or insulin resistance. In fact, low-glycemic diets are one of the best choices for people who have metabolic syndrome since they have to stabilize insulin levels.
The Bottom Line?
All calories aren’t created equal, and it’s important to take a balanced approached when choosing a diet for weight loss. Diets that restrict most carbs may increase energy expenditure, but they’re hard to maintain and place your body under greater stress. Low-carb diets are effective for weight loss, but a significant number of people gain back most of the weight they lose while on them. Low-fat diets restrict healthy fats like monounsaturated and omega-3 fats that are heart-healthy and waistline-friendly. A low-glycemic diet takes a more balanced approach by emphasizing fiber-rich carbs like vegetables and whole grains and healthy sources of fat and protein. It’s a healthier option.
References:
Medscape.com “Not All Calories Are the Same, New Research Finds”
JAMA 2012: 307: 2627-2634.
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