What to Make of Low-carb Promises?
Widely covered research published this year has found that a low-carb diet is a more effective weight loss tool than a low-fat diet. But does this mean we should always favor fat to carbs?
The U.S. population generally knows about bad carbs and good fats. Certainly the health conscious know that all carbs are not created equal, and while refined carbohydrates contain much needed energy for both endurance and speed workouts, they are not as beneficial as whole grains, legumes and other unprocessed, more fibrous carbohydrate sources. One reason is the stable release of whole grains over a longer period of time, without the metabolic peaks and crashes associated with highly glycemic carb sources.
Recent attempts to decriminalize it notwithstanding, most of us are also well aware that saturated fat comes with its own set of complications, including its high caloric cost and propensity to raise body cholesterol level (whose elevation has more negative consequences than a raised dietary level, e.g., cholesterol intake from otherwise healthy shrimp). Much is made, on the other hand, of the cholesterol-lowering, heart-healthy attributes of “good fats” like those found in salmon, seeds, nuts and certain vegetable oils.
But sugar's image has suffered in the past decade or so, as the nation better realizes the profound lack of nutritional value, heavy caloric expense and disconcerting ubiquity of it in the modern human diet. So are carbs getting a bad rap because they convert so easily to sugar, or because many carbohydrate-rich foods are also loaded with sugar? It pays to take a closer look at what the research currently says and does not say about the matter.
Why more weight loss?
The original paper from the Annals of Internal Medicine that started all the carb-vs.-fat fuss concluded that, for obese adults, “The low-carbohydrate diet was more effective for weight loss and cardiovascular risk factor reduction than the low-fat diet. Restricting carbohydrate may be an option for persons seeking to lose weight and reduce cardiovascular risk factors.”
Roughly 150 obese adults who were otherwise healthy were randomized to eat either a less-than-30-percent-fat diet or a diet of less than 40 grams of carbohydrate per day. At 12 months, the low-carb group had lost nearly 8 lbs more than the low-fat group, even though caloric intakes were similar. The low-carb group also saw greater improvements in body composition, CRP levels (which rise when inflammation is present in the body), HDL (“good”) cholesterol, and triglyceride levels.
Yet as one MD noted in the comment section of the online publication, “The caloric intake of participants in the two groups was said to be similar, but the low-carb group reported an average intake of 1,448 calories at 12 months (table 2), which is 79 calories per day less than the low-fat group. over the 365 days of the study, that totals 28,835 calories. At 3,500 calories/lb, that equals 8.24 lb, slightly more than the entire difference in weight loss between the two groups. This extra weight loss might also have been responsible for some of the other differences in risk factor between the groups. There is a message here for dieters: if you cut back a small number of calories every day, you will lose a substantial amount of weight in a year.” That is a fairly unassailable analysis that should certainly help people see the benefit of any caloric reduction to which you add a good deal of time.
Adopt what you can sustain
A few days later, a meta-analysis was published in JAMA that suggested either diet would be effective, and that recommendations should be based on likely adherence. In that study, popular branded low-carbohydrate and low-fat diets were found to lead to significant weight loss, with little difference between the two approaches.
Researchers examined data from 48 randomized trials that studied various popular diets among roughly 7,300 overweight or obese adults. They found that all diets were superior to no intervention. In particular, low-carb programs (e.g., Atkins) and low-fat approaches (e.g., Ornish) yielded the greatest weight loss at six months (roughly 17.6 lbs versus no diet), with minimal differences among the individual diets. Weight loss at six months was somewhat lower with moderate macronutrient diets (e.g., Weight Watchers), at 15 lbs.
The authors say their analysis "supports the practice of recommending any diet that a patient will adhere to in order to lose weight."
What kind of weight loss?
So how do we implement all of this research practically? For starters, note that in the low-fat vs. low-carb study, while the low-fat group did lose weight, they lost more muscle than fat. In fact, the low-fat group lost significant lean muscle mass, and since your balance of lean mass versus fat mass is much more important than weight, this finding should not be swept under the carpet.
The high-fat group followed something of a modified Atkins diet. They were told to eat mostly protein and fat, and to choose foods with primarily unsaturated fats like fish, olive oil and nuts. But they were allowed to eat foods higher in saturated fat as well, including cheese and red meat.
Over all, they took in a little more than 13 percent of their daily calories from saturated fat, more than double the 5 to 6 percent limit recommended by the American Heart Association (AHA). Do note that the majority of their fat intake, however, was unsaturated fat.
The low-fat group included more grains, cereals and starches in their diet. They reduced their total fat intake to less than 30 percent of their daily calories, which is in line with the federal government’s dietary guidelines. The other group increased their total fat intake to more than 40 percent of daily calories.
Both groups were encouraged to eat vegetables, and the low-carbohydrate group was told that eating some beans and fresh fruit was fine as well.
Still, those on the low-carbohydrate diet ultimately did so well that they managed to lower their Framingham risk scores, which calculate the likelihood of a heart attack within the next 10 years. The low-fat group on average had no improvement in their scores.
So is the trouble carbohydrate?
Eating refined carbohydrates tends to raise the overall number of “bad cholesterol” LDL particles and shift them toward the small and dense variety, which contributes to atherosclerosis. Saturated fat tends to make LDL particles larger, more buoyant and less likely to clog arteries, at least when carbohydrate intake is not high.
Small, dense LDL is the kind typically found in heart patients and in people who have high triglycerides, “central obesity” (think apple- as opposed to pear-shaped) and other aspects of metabolic syndrome. Ronald M. Krauss, MD, is the former chair of the AHA's committee on dietary guidelines and also the director of atherosclerosis research at Children’s Hospital Oakland Research Institute. He told the New York Times:
“I’ve been a strong advocate of moving saturated fat down the list of priorities in dietary recommendations for one reason: because of the increasing importance of metabolic syndrome and the role that carbohydrates play.”
So perhaps sugar—and certainly sedentarism—is the culprit.