When it comes down to what to eat for optimal health and weight, it’s not black and white—as evidenced by two recent studies that produced somewhat mixed results. One study, published in the Journal of the American Medical Association, appears to suggest that a high-protein, low-carbohydrate diet produces the best metabolic response and energy expenditure for the maintenance of weight loss.[i] In contrast, a study published in the British Medical Journal indicates that a high-protein, low-carbohydrate diet increases the risk of cardiovascular disease.[ii]
Over the past few decades, carbohydrates have been labeled as “good” or “bad” depending on the latest dietary trends. And carbohydrates aren’t the only target—at different times, fad diets have both ostracized and revered protein and fat as well. Never before has something so basic—feeding ourselves—been so complicated. Between government recommendations, the food pyramid, and an arsenal of contradictory research, the question remains—what should we eat? The answer, it turns out, is not so simple—and depends a great deal on how you interpret the research.
A Little Background
To understand food and how it works in the body, it’s important to understand the basics. The many nuances of nutrition can be complex and overwhelming, but to simplify—food is comprised of three macronutrients (protein, fat, and carbohydrates) and a wide array of micronutrients (vitamins and minerals). Despite science’s ongoing efforts to analyze these dietary components separately, the fact is that they work together, each playing a critical role to fuel and nourish the body.
To understand the implications of these two most recent studies, it’s important to have a basic understanding of calories and the glycemic index.
Calories: A calorie is simply a unit of measurement. By definition one calorie is the energy it takes to raise the temperature of 1 gram of water 1 degree Celsius. In other words, calories are energy. The energy from calories fuels our bodies similar to the way gasoline fuels a car.
Glycemic index: The glycemic index (GI) is a measure of the effects of carbohydrates on blood sugar levels. Carbohydrates that break down quickly and thus release glucose into the bloodstream quickly, have a high GI (also referred to as glycemic load); whereas carbohydrates that break down slowly, releasing glucose into the bloodstream gradually, have a low GI.
The glycemic index was originally designed as a tool for diabetics because a lower glycemic response typically results in a lower insulin demand; however, the index is a useful tool for everyone. Glucose is considered the reference food and has a value of 100. To put it into perspective—a baguette has a value of 95 and chickpeas have a value of 33.
Rather than lumping carbohydrates into the general categories of “good” or “bad”, it might make more sense to categorize carbohydrates based on glycemic load. Lower glycemic carbohydrates may be a healthier choice than high-glycemic foods.
The JAMA Study
The study recently published in JAMA was designed to examine the energy expenditure and metabolic responses that resulted from three different diets. The study included 21 overweight and obese young adults who initially underwent a standard low-calorie diet until they achieved a 10 to 15% weight loss. After this initial weight loss, the subjects were placed on one of three diets:
- A low-fat diet with high glycemic load and 20% of energy from protein (60% of energy from carbohydrate, 20% from fat, 20% from protein; high glycemic load)
- A low–glycemic index diet with moderate glycemic load and 20% of energy from protein (40% from carbohydrate, 40% from fat, and 20% from protein; moderate glycemic load)
- A very low-carbohydrate diet with low glycemic load and 30% of energy from protein. (10% from carbohydrate, 60% from fat, and 30% from protein; low glycemic load)
The subjects remained on the assigned diet for 4 weeks and researchers measured their resting energy expenditure (REE) and total energy expenditure (TEE). The premise was that the higher the energy expenditure, the higher the weight loss or maintenance of weight loss. In other words, if REE and TEE declined, subjects would be more likely to gain back the weight lost. Both REE and TEE did decline with all diets, but declined the most with the low-fat, high-glycemic diet—which might seem to suggest that a low-carbohydrate, high-protein diet is the best option for maintaining weight loss; however, there are some important factors to consider.
Although the very low-carbohydrate diet produced the best metabolic response, it also came with some unwelcome hormonal changes, namely higher levels of cortisol (a stress hormone) and CRP (a marker of inflammation). In contrast, the low-glycemic diet produced metabolic benefits without those signs of physiological stress and chronic inflammation. In other words, glycemic load might be the key. The research seems to suggest that rather than “no carbs”, it’s important to choose the right carbs.
The BMJ Study
The study recently published in the BMJ was designed to examine the long-term consequences of a low-carbohydrate, high-protein diet on cardiovascular health. The study included a random sample of 43, 396 Swedish women ages 30 to 49 who completed an extensive dietary questionnaire and were followed for an average of 15.7 years.
The researchers used the data to create a 20-point scale, with higher scores indicating a lower ratio of carbohydrates to protein. They found that with each increase of 2 points on the scale, women had a 5% increase in cardiovascular events. They concluded that: “Low-carbohydrate, high-protein diets used on a regular basis and without consideration of the nature of carbohydrates or the source of proteins, are associated with increased risk of cardiovascular disease.”
To summarize—a low-carbohydrate diet may have both pros and cons, but uncertainties remain. Perhaps such a diet produces a beneficial metabolic response, but perhaps it also increases the risk of heart disease. Deeper examination of the data reveals that there are a variety of factors at play, including the importance of glycemic load.
Neither study leads to the conclusion that carbohydrates are good or bad. In fact, in an editorial accompanying the JAMA study, George A. Bray, MD says, “Although the exact relationship between dietary composition and weight maintenance remains unclear, calorie restriction is more important than diet composition in administering weight loss regimens.”[iii]
The bottom line—we may never be able to isolate nutrients and determine the ideal diet, if in fact there is such a thing. However, common sense seems to dictate that real food—in the form of whole grains, fruits, vegetables, and animal products—is the optimal foundation of a healthy diet. Balance remains the key.
In the end, Michael Pollan may have summed it up best: “Eat food. Not too much. Mostly plants.”[iv]
[i] Ebbeling CB, Swain JF, Feldman HA, et al. Effects of dietary composition on energy expenditure during weight-loss maintenance. Journal of the American Medical Association. 2012; 307(24): 2627-2634.
[ii] Lagiou P, Sandin S, Lof M, et al. Low carbohydrate-high protein diet and incidence of cardiovascular diseases in Swedish women: A prospective cohort study. British Medical Journal. 2012; 344: e4026.
[iii] Bray GA. Diet and Exercise for Weight Loss. Journal of the American Medical Association. 2012; 307(24): 2641-2642.
[iv] Pollan, M. Food Rules: An Eater’s Manual. Penguin Books, 2009.