Dueling Diets: Protein vs. Carbs

A few years ago, high-protein (HP), low-carbohydrate (LC) weight-loss diets experienced a resurgence, coinciding with concerns about escalating obesity and its potentially negative health outcomes. Most credit the late Dr. Atkins as the father of HP-LC diets for weight loss. In reality, Dr. William Harvey, a 19th Century ear, nose and throat specialist, and William Banting, a carpenter-undertaker, experimented with this approach in 1862. The “Banting Diet” was not well received by the medical profession, much like the Atkins diet. Today, the debate rages on. One side asserts that empirical data from a multitude of followers support this type of diet; the other side declares that no studies on its long-term safety exist.

Many popular diets, such as the South Beach diet, Sugar Busters and the Atkins Diet, typically include high protein; restricted carbohydrates — especially refined sugars and flours; unlimited calories and sometimes unlimited fat, and a book to exalt the diet’s virtues while guiding new followers in its practice.

Proponents of HP-LC diets base their recommendations on the metabolic effects of carbohydrates on blood sugar and insulin. They view carbohydrate consumption as the source of a cascade effect that goes from increased blood sugar to insulin release to fat storage. Their position is that protein and fat do not contribute to fat deposition because they do not raise blood sugar or induce insulin release.

In HP diets, allowed carbohydrates can include fruits, vegetables and fiber-containing grains that add little or nothing to the glycemic load. The Atkins diet employs a “Net Carb” concept that subtracts the non-glycemic carbohydrates, such as fiber and polydextrose, from the total carbohydrates in rating foods.

Recent peer-reviewed studies report positive results and/or lack of expected negative consequences from HP-LC diets. Research from the University of Illinois at Champaign, published in the February 2003 Journal of Nutrition found that a diet moderately high in protein with a 1:4 carbohydrates to protein ratio (CHO:PRO) resulted in similar weight loss in women as did a conventional weight-loss diet containing moderate protein with a 3.5 CHO:PRO. However, the women on the moderately high protein and reduced CHO:PRO diet lost more body fat and less muscle mass with more stable blood glucose, reduced insulin response to meals, lower triglycerides and greater satiety than the control group. Principal investigator, Donald Layman, suggests that leucine, an essential amino acid found in high-quality proteins, may play a metabolic role in regulating glucose homeostasis and weight loss.

Two other studies from the May 22, 2003 issue of the New England Journal of Medicine measured LC diets against a calorie- and fat-restricted diet in obese men and women. In a six-month study of individuals with diabetes or metabolic syndrome, LC diets produced more weight loss accompanied by improvements in triglycerides and insulin sensitivity. The second study, a multicenter, randomized one-year trial, compared a HP-LC high-fat diet with a conventional high-carbohydrate, low-fat diet. Initial weight loss was higher with the HP-LC diet but was not significantly different at one year. Again, risk factors for cardiovascular disease improved with a decrease in triglycerides and an increase in HDL-cholesterol.

Other research examined calcium retention and renal function in women to answer critics’ concerns about bone loss and kidney damage from high-protein intakes. No negative effects were found, except in those with mild renal insufficiency. In the July 2003 American Journal of Clinical Nutrition, researchers reported that a diet with high-protein (27% of calories) from meat, poultry and dairy foods resulted in similar weight and fat loss, but less lean mass loss, and improved glycemic response and triglyceride levels when compared to a standard (16%) protein diet in overweight and obese hyperinsulinemic subjects. No change was observed in markers of bone turnover, calcium excretion and blood pressure.

While support for the theories behind HP diets is mounting, researchers still advise caution when interpreting data. Most of the studies are small and need replication on a larger-scale over longer time. Additionally, dropout rates were high in longer-term studies and actual differences between groups were small.

Critics of the Atkins diet and similar plans argue that in reality, these diets are calorie-restricted diets. A systemic review of research on LC diets from Jan. 1966 to Feb. 2003, published in the April 2003 Journal of the American Medical Association, supports this view. The review notes that longer diet duration and calorie restriction is associated with weight loss, but carbohydrate reduction isn’t. It also notes no adverse effect on lipid, glucose, insulin levels or blood pressure from LC diets. The conclusion: no recommendation for or against these diets is possible.

Additionally, critics claim that maintaining HP-LC diets is harder than conventional weight-loss diets, with those experiencing quick success frequently regaining at least all the lost weight. Others dispute the premise that low-fat diets helped create the current obesity crisis and cite an increase in per capita consumption of fat, sugars, and calories accompanied by less physical activity as the real cause of weight gain.

Today, demand for HP-LC foods and beverages in restaurants and supermarkets, including commodity foods such as beef and eggs, is on the rise, with many new HP-LC products appearing regularly. Ingredients such as polydextrose and resistant starches help achieve taste and texture goals without a glycemic load. Some niche companies produce only these products, while mainstream manufacturers and restaurateurs are jumping on the bandwagon with line extensions and new offerings.

Until solid, scientific research sorts out the realities of what diet is best for maintaining a healthy weight, consumers will choose foods based on their beliefs of what works for them. Only time will tell if HP-LC diets are a passing fad or a new way of life.

Angela M. Miraglio ([email protected]) is a registered dietitian and Fellow of the American Dietetic Association from Des Plaines, IL. Her firm, AMM Food & Nutrition Consulting, provides communications and technical support to food and beverage companies and associations.