What's better for weight-loss: Cutting carbs or fat?
Lately, it seems everyone is riding the low-carb bandwagon – ditching pasta, forgoing fruits and eating their sandwiches as lettuce wraps. But according to a new Cell Metabolism study, opting for a low-fat diet might actually lead to better fat-loss results.
For the study, researchers with the National Institutes of Health examined the effects of low-carb and low-fat, calorie-controlled diets on 19 obese men and women, none of whom had diabetes. During the study, the participants stayed at the NIH's metabolic unit around the clock, so researchers could regulate and record everything they did – and what they ate. Each group cut their overall caloric intake by 30 percent, half of them by cutting carbs and half of them by cutting fat.
While the reduced-carb dieters lowered their levels of insulin as well as lost slightly more weight than those who cut fat, the reduced-fat dieters actually lost more body fat than the carb-cutters.
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"The reason this happened relates to the balance between how much fat is eaten and burned by the body," explains lead author Kevin Hall, a senior investigator with the NIH's National Institute of Diabetes and Digestive and Kidney Diseases. On the low-fat diet, participants experienced a greater difference in the amount of fat they were eating and the amount of fat their bodies were burning compared to those who cut carbs.
The Low-Carb Controversy
"There is a popular theory that claims low-carb diets are particularly effective for fat loss because they decrease levels of the hormone insulin, thereby increasing the amount of fat that's released from fat tissue. Some people even claim that without reducing insulin it is not possible to reduce body fat," Hall says. "The results of our study run counter to this theory and suggest there is not a metabolic advantage of a low-carb diet."
However, past research has largely pointed to low-carb diets as the better fat-burner, a fact that critics of the study are quick to mention. For example, one 2014 Annals of Internal Medicine study of 148 obese men and women found that participants who ate a low-carb diet for one year lost 7.7 pounds more than those who had been eating less fat. However, Hall points out that in these longer studies, researchers can't really be sure of what the participants were and weren't eating over the course of the study.
"As evidenced from multiple recent meta-analyses, studies consistently show that on average a low-carbohydrate diet does better than a low-fat diet in terms of weight loss and fat loss, and several cardio-metabolic markers," says low-carb advocate Jeff Volek, a registered dietitian and professor of human sciences at The Ohio State University. "A major reason people have better results with low-carb diets is because they promote greater satiety and people eat less." He also notes that low-carb diets are especially beneficial to people who are insulin resistant, meaning their blood sugar level excessively rise in response to carbohydrate consumption. "In reality, each person has a level of carbohydrate tolerance, and staying under that level is an effective method to maintain good health," Volek says.
Pam Bede, a registered dietitian and board-certified specialist in sports dietetics with Abbott's EAS Sports Nutrition, also notes that low-carb diets have been shown to help control diabetes, high blood pressure and cardiovascular disease. They also improve HDL cholesterol and triglyceride values better than moderate-carb diets do.
"However, low-carb dieters must understand that carbs give your body fuel to function, especially when you're working out. Anyone who is moderately to highly active should include some carbs in their diet to stay energized," Bede adds. "If you work out regularly or are staying active to facilitate weight loss, eating too few carbs from a low-carb diet can cause fatigue and decrease your athletic performance. Carbs are a primary source of fuel for your workout – if you run out of steam quickly at the gym, you may head home early and therefore do yourself and your weight loss a disservice. You may opt to do fewer reps, run for a shorter period of time or pay less attention to safe exercise form because your body doesn't have the fuel it needs to continue."
She recommends that even those dieters who are following a low-carb eating plan consume carb-containing foods such as fruit, yogurt or trail mix before hitting the gym to get the greatest weight-loss benefit from their workouts.
Cutting Through the Fat
Meanwhile, although consuming some fat is anything but unhealthy – unsaturated fat promotes healthy metabolic functioning, and a recent Annals of Internal Medicine meta-analysis of 512,420 people concludes that eating more saturated fat may not increase your risk of heart disease – slightly reducing your overall fat intake can cut calories much more easily than can cutting carbs. One gram of carbohydrates contains four calories, while 1 gram of fat contains nine.
"Low-fat diets might be your best route if you want to eat a variety of foods in moderation. A low-fat diet includes fruits, vegetables, whole grains and proteins like lean meat and fish," Bede says. It really just reduces your intake of high-fat animal products like steak (although grass-fed beef contains less fat), cream, cheese and butter.
"Low-fat dieters need to remember the body requires some healthy fats to maintain the immune system, regulate vital organs and keep good cholesterol levels up. They also help regulate insulin levels, which make you feel more satisfied after a meal than consuming protein and carbs alone," Bede says. She recommends that, even when on a low-fat diet, men and women consume at least 26 grams of unsaturated fat per day.
Which Would You Rather Cut?
Meantime, a recent review of 59 studies on the low-carb, low-fat debate published in The Journal of the American Medical Association reported that while both diets led to significant weight loss, the low-carb diet led to moderately more pounds shed. Still, the researchers concluded that the effect was small enough that dieters are best off following the strategy that best fits their lifestyle.
After all, to some people, cutting carbs is painless and easy to do over the long term. To others, the thought of forgoing regular pasta nights is almost too much to bear, Hall says. To others, low-fat is synonymous with low-flavor. Maybe they can reduce their fat intake for a couple of weeks or months, but to lose the weight and keep it off, the change has to endure.
"Low-carb diets vs. low-fat diets fuel a constant debate in the nutrition community," Bede says. "Each has their own pros and cons, but when it comes to effectiveness, one stands out over the other: whichever diet you can personally sustain."
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