By Marie Spano, MS, RD, CSCS, CSSD
The cause of obesity is clear. We are eating more calories than we are burning, according to both the CDC and the World Health Organization. Yet decades worth of public health messages and weight-loss programs based on cutting calories and increasing physical activity haven’t made a dent in the obesity epidemic. And this simple, yet obvious fact has many experts questioning the accuracy of this age-old energy balance equation. Is excessive calorie intake the real culprit? Or, does the obesity problem lie in what we are eating as opposed to how many calories we are consuming?
Chronic Carb Consumption
Some scientists and health professionals are targeting what we are eating, specifically carbohydrates, as the cause of the obesity epidemic, throwing them to the birds like day-old stale bread. Eat carbohydrates, especially syrupy sodas and sweet treats, and your blood sugar will rise, signaling your pancreas to release insulin, which will quickly lower blood sugar by increasing uptake of sugar (glucose) by muscle and fat. Insulin also decreases the breakdown of fat in fat tissue while increasing the transport of the sugar from your caramel latte into fat cells— initiating the production of fat for storage. According to the anti-carbohydrate crowd, chronic consumption of carbohydrates keeps insulin levels up and your body busy churning out fat tissue. And for people with insulin resistance, a condition that leads to even greater production of insulin because the body doesn’t use insulin effectively, consuming too many carbohydrates can make it very difficult to lose weight, thanks to an abundance of insulin in the bloodstream. So the solution seems very simple: cut out carbohydrates in favor of protein and fat and you’ll quickly drop weight. And if metabolism and endocrinology were that simple and we all loved a diet of steak, eggs and butter, life would be a whole lot slimmer. Unfortunately, this isn’t the case.
Insulin and Fat Storage
Cutting carbohydrates makes a lot of sense when you consider the actions of insulin. However, the immediate action of insulin after a meal does not take into account what happens over the course of time. Let’s say you devour a cinnamon raisin bagel slathered with jam. Your blood sugar will shoot up and your pancreas will release insulin. If you aren’t in the midst of hardcore physical activity and therefore you don’t need the immediate 400-plus calories of energy you just ate, your body will store a large portion of these calories as fat. But, if later in the day you are in a calorie deficit, having burned more calories than you consumed, your body will burn stored fuel, from body fat, for energy. So, you’ll tap into your fat stores for fuel when your body hasn’t had enough calories to keep up with your daily needs. And therefore, just because insulin may shuttle sugar out of your bloodstream and into fat tissue in the short term, this hormone isn’t the sole determinant of how much fat you have on your body. To gain weight, you still have to overconsume calories or your body will use the carbohydrate you are eating (or the stored body fat) for energy.
Low-Calorie Weight Loss
Research backs up the importance of calories for weight loss while questioning the demonization of carbohydrates. In fact, several research studies using many different types of participants (from obese postmenopausal women to men) show that calorie-controlled diets including plenty of carbohydrates lead to weight loss if the participants follow them. Studies have also found participants can lose weight on a low-fat, high-carbohydrate ad libitum (eating when hungry without counting calories) diet. And, one study comparing the two approaches— a reduced calorie low-fat, higher carbohydrate diet and a reduced-calorie, low-carbohydrate diet— found both resulted in weight loss in overweight and obese adults over an eight-week period, with no significant differences in weight loss between the diet groups. So the clear winner seems to be total calories.
Yet this research combined with a closer look at calorie balance over time versus the immediate actions of insulin only still doesn’t explain the success of low-carbohydrate diets. Could there be more to them than meets the eye, especially if they control for total calorie intake while cutting down on carbohydrates?
Appetite-suppressing Protein
What do the Atkins, South Beach and the Paleo diets all have in common, aside from excluding certain types of carbohydrates and therefore decreasing total carbohydrate intake? First off, eliminating certain types of carbohydrates takes a lot of guesswork out of dieting. You won’t have to cut a perfect 200-calorie slice of cake or estimate how many cookies fit into your calorie budget because both are off limits on carbohydrate-controlled diets. Plus, if you don’t eat these foods in the first place, you won’t be tempted by second servings. But, more importantly, the majority of low-carbohydrate diets are also high in protein. And, protein has three primary benefits in the war against fat.
Protein is the most satiating of the three macronutrients— protein, carbohydrate and fat. During digestion, protein quickly triggers a cascade of events leading to appetite-suppressing signals sent to the brain so you feel full. In fact, protein seems to increase satiety in a dose-dependent manner, though scientists haven’t figured out the “magical dose” of protein necessary to maximally stimulate satiety. However, when you cut carbs, you’ll likely increase your protein intake (unless you are on a ketogenic diet). In addition to keeping you full, protein has a greater thermic effect of feeding— you will burn more calories digesting protein than carbohydrate or fat.
And finally, protein preserves metabolically active lean muscle mass during weight loss. When on a reduced-calorie weight-loss diet, you need more protein in your diet to preserve lean tissue. Low-carbohydrate diets automatically provide more protein, whereas traditional low-fat diets do not. And, muscle is important for weight control because it burns more calories than fat tissue, even when you are sitting at your desk typing away at your computer. Skeletal muscle also helps regulate blood sugar levels.
Carbs Versus Calories Experiments
Low-carbohydrate diets work, especially for those who are insulin resistant. And, these diets may also facilitate greater weight loss in obese individuals. However, the focus on carbohydrates may be less important than ramping up protein intake. So which method should you choose? The debate about carbohydrates and calories has led to divergent scientific opinions and therefore, very different approaches recommended for weight loss. And because several questions still need to be answered, researchers from the Nutrition Science Initiative will delve into the fine details about calories and carbohydrates through a carefully designed a set of well-controlled experiments. First the scientists will feed overweight and obese adults a typical American diet, controlling for every calorie consumed, while determining their exact calorie needs to maintain weight. After this part of the study, they will dramatically decrease the carbohydrate content of their diet to as close to zero as possible by including only the carbohydrates naturally occurring in meat, poultry, chicken, eggs, cheese, fats and green vegetables. The aim: suppress insulin levels as much as possible while feeding the participants the total calories they need to maintain weight.
During both parts of the study, protein intake will be kept constant to account for the thermic effect of feeding. If their weight stays the same, then calories are the primary factor determining weight loss. If they lose weight, then carbohydrate-mediated increases in insulin play a crucial role in weight loss in overweight and obese adults.
Like any rigorous scientific study, this will take some time— years, in fact, to set up the studies, recruit participants, perform the studies, evaluate the results and publish the findings. And, as any scientist starts digging for answers, sometimes more questions emerge. But at some point, we’ll have a clearer winner in the calories versus carbohydrate debate. And once this debate is settled, we’ll have to test approaches to executing the diet in real life— a daunting task, especially if the high-fat, moderate protein, low-carbohydrate diet comes out on top.
Choosing a Diet
Until these studies are carried out, it’s important to rely on what we know right now. And, the weight loss research to date has shown there are multiple dietary approaches that work. Diets should be individualized, taking into account lifestyle habits, medical history (including diabetes, insulin resistance, other diseases and medical concerns), diet history and food preferences. As the debate about macronutrient content is going on, keep in mind that the most important factor that will determine weight loss and improved health outcomes on any diet is adherence. So, choose the diet plan that you can stick with until the weight comes off.
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