Two studies involving low-carb diets made headlines this week. One suggested a low-carb diet may provide a metabolic advantage, while the other suggested a low-carb diet may kill you.
Let’s start with the good news:
A new study is raising questions about the age-old belief that a calorie is a calorie.
The research finds that dieters who were trying to maintain their weight loss burned significantly more calories eating a low-carb diet than they did eating a low-fat diet.
The study, funded by the National Institutes of Health, was designed to see if changing the type of diet people consumed helped with weight maintenance because dieters often regain lost weight.
So scientists had 21 obese participants, ages 18 to 40, lose 10% to 15% of their initial body weight (about 30 pounds). After their weight had stabilized, each participant followed one of three different diets for four weeks. Participants were fed food that was prepared for them by diet experts. The dieters were admitted to the hospital four times for medical and metabolic testing.
The diets had the same number of calories, but the fat, protein and carbohydrate content varied. Those diets:
•A low-fat diet which was about 20% of calories from fat and emphasized whole-grain products and fruits and vegetables.
•A low-carb diet, similar to the Atkins diet, with only 10% of calories from carbohydrates. It emphasized fish, chicken, beef, eggs, cheese, some vegetables and fruits while eliminating foods such as breads, pasta, potatoes and starchy vegetables.
•A low-glycemic index diet, similar to a Mediterranean diet, made up of vegetables, fruit, beans, healthy fats (olive oil, nuts) and mostly healthy grains (old-fashioned oats, brown rice). These foods digest more slowly, helping to keep blood sugar and hormones stable after the meal.
Findings, published in this week’s Journal of the American Medical Association: Participants burned about 300 calories more a day on a low-carb diet than they did on a low-fat diet. “That’s the amount you’d burn off in an hour of moderate intensity physical activity without lifting a finger,” says senior author David Ludwig, director of the New Balance Foundation Obesity Prevention Center at Boston Children’s Hospital.
Now, before we all jump up and down and yell “Hallelujah!” we should keep in mind that a study population of 21 is pretty small. The smaller the study population, the more likely a significant difference in the results is due to chance. That’s just basic statistics. If I flip a coin four times and it comes up heads three times, I can’t declare that my coin will come up heads 75% of the time. My sample size was too small. If it comes up heads 750 times out of a thousand, now we’re talking.
With that caveat out of the way, it was a controlled clinical study and does suggest a low-carb diet might provide a metabolic advantage. That would certainly fit with my experience. I always found it difficult to lose more than 10 pounds on a low-fat diet, and I had to put up with being hungry most of the time to achieve even that modest result.
I wasn’t hungry while losing weight on a low-carb diet, and this study hints at what I believe is the reason: fuel availability. If you burn more calories on a low-carb diet than on a low-fat diet, even at the same caloric intake, then your body is either storing less of what you eat or tapping more of what you’ve already stored. Either way, your cells are getting more fuel, which means your body is less likely to slow your metabolism in response to what it considers a fuel shortage.
I think it’s significant that the dieters had already lost an average of 30 pounds before being divided into the three diet groups. To keep your blood sugar within the biologically safe range, your body needs to switch between storing fatty acids when blood sugar goes up (so you’ll burn the excess glucose first), then releasing fatty acids as blood sugar goes down (so it doesn’t drop too low).
I believe what some people call a set point is related to our ability to release fatty acids at a rate sufficient to supply us with fuel when blood sugar begins to fall. Obese people release as many fatty acids on average as non-obese people, but here’s the kicker: they require more fat mass to do so. Each unit of fat releases fewer fatty acids, so they need more body fat to release the same number of fatty acids as a thin person. So at some point, shrinking the fat mass means releasing fewer fatty acids than the body needs to keep blood sugar stable. That’s when the body rebels and slows down the metabolism (and ramps up hunger) instead of allowing the glucose/fatty-acid balancing act to go all out whack.
Obese people who’ve already lost 30 pounds are more likely to be approaching the point of biological rebellion than people who just started dieting. That’s where the low-carb diet might provide a metabolic advantage. By keeping insulin levels lower, the low-carb diet would enable a dieter’s shrinking fat mass to continue releasing fatty acids at the necessary rate. No fuel shortage, no cellular-starvation response, no slowing of the metabolism.
Naturally, The Usual Suspects don’t agree:
George Bray, an obesity researcher at Pennington Biomedical Research Center in Baton Rouge who has also studied this topic and who wrote the accompanying editorial in JAMA, says that other studies “show that you can do well on any diet as long as you stick to it. Adherence is the major key for weight loss and maintenance. There is no magic in any diet.”
Fuel availability isn’t about magic, Dr. Bray. It’s about biochemistry.
George Bray is what I’d call an intelligent imbecile. He’s been promoting high-carb and low-salt diets for years and plays games with his study designs and data to support his beliefs. It was Bray, for example, who declared that macronutrient ratios make no difference for weight loss — after he conducted a study in which protein and fat intake were altered, but carbohydrate intake stayed the same. (Uh … wouldn’t you want to try messing with that variable too?)
It was also Bray who conducted the study of salt and hypertension that I mentioned in my Science For Smart People speech. He put two groups of people on two different diets. One diet was high in sugar and other junk, the other was more like a Mediterranean diet with lots of vegetables and no sugar. Bray had each group consume a lot of salt with their diets for several weeks, then measured their blood pressure. Then he had each group consume very little salt with their diets for several weeks and measured their blood pressure again. Within each group, the average drop in blood pressure after severely restricting salt was slightly less than three points. Whoopie.
That wasn’t the result Bray wanted, so in the study’s conclusions he compared blood pressure readings for the junk-food dieters after their high-salt phase to the blood pressure readings for the Mediterranean dieters after their low-salt phase, found a significant difference, and declared it evidence that salt causes high blood pressure. That’s like comparing the livers of heavy drinkers who consume a lot of salt to the livers of moderate drinkers who consume very little salt and declaring that salt causes liver damage.
But enough about Bray. There’s more bad science to dissect in the other study that hit the news this week:
Women who regularly eat a high-protein, low-carbohydrate diet may be raising their risk of heart disease and stroke by as much as 28 percent, a new study suggests.
Although the absolute increase in risk is small — four or five extra cases per 10,000 women — many young women try the Atkins diet or similar regimens and could be setting themselves up for cardiovascular problems later in life, the researchers noted.
“Low-carbohydrate, high-protein diets are frequently used for body-weight control,” said lead researcher Dr. Pagona Lagiou, assistant professor of epidemiology at the University of Athens Medical School in Greece. “Although [the diets] may be nutritionally acceptable if the protein is mainly of plant origin, such as nuts, and the reduction of carbohydrates applies mainly to simple and refined [carbohydrates] like unhealthy sweeteners, drinks and snacks, the general public does not always recognize and act on this guidance.”
That’s because we recognize the guidance as bull@#$%, Dr. Lagiou. People weren’t living mainly on plant proteins back when rates of heart disease were much lower.
For the study, Lagiou’s team collected data on the diets of more than 43,000 Swedish women who were between the ages of 30 and 49 at the start of the study.
Over an average of 15 years of follow-up, there were more than 1,200 cardiovascular events, including heart disease and stroke. There were more of these events among the women who followed a high-protein, low-carbohydrate diet than among women who didn’t, the researchers found.
Compared with women who veered furthest from the high-protein, low-carbohydrate diet, women who followed the diet most closely increased their risk by 28 percent, even after other risk factors, such as smoking, drinking, hypertension, exercise and fat intake, were taken into account, the researchers noted.
I’m sure you’ve already spotted this study for what it is: an observational study (strike one) based on food-recall questionnaires (strike two). We don’t know if the participants accurately recalled what they’d been eating over the years (not likely), we don’t know what kinds of fats the so-called Atkins dieters consumed, and we don’t know if the people on the “high protein” diet ate a lot of meat because they believed it was good for them, or if they’re don’t-give-hoot types who believed red meat is bad for them but ate it anyway. Those are two totally different types of people. Since this study began 15 years ago, long before the low-carb/high-fat craze took off among health-conscious Swedes, I vote for the latter.
Another expert, Samantha Heller, an exercise physiologist and clinical nutrition coordinator at the Center for Cancer Care at Griffin Hospital in Derby, Conn., said “the results of this study are not surprising.”
Popular high-protein diets inevitably include an abundance of cheese and red and processed meats, and a dearth of healthy carbohydrates such as whole grains, vegetables, legumes and fruits, she said.
First off, Ms. Heller, the low-carb diets most advocates recommend aren’t “high-protein.” They’re high-fat. And secondly, why it is “inevitable” that those diets will include an abundance of cheese and processed meats? I eat a bit of cheese and almost no processed meat whatsoever. And if you believe whole grains are “healthy carbohydrates,” I suggest you read Wheat Belly.
Someone sent me a link to the full study, so I read it. Here are some interesting numbers if we choose to assume (for no apparent reason) that the food-recall questionnaires were an accurate accounting of what people ate.
The researchers divided the women into groups based on carbohydrate and protein intake, but not fat intake. So their scale went from high-carb/low-protein to low-carb/high-protein. The researchers declared that the Atkins-type diet increased risk of heart disease and stroke, but the figures for strokes are laughable. In the high-carb diet group, there were 3.1 ischemic (blood clot) strokes per 10,000 women. In the high-protein group, there were 5.2 per 10,000 women. So the actual difference (as I like to pound home in Science For Smart People) is 2.1 ischemic strokes for every 10,000 women. If we take those odds and express them as percent, here’s what we get:
High-carb diet: 0.031%
High-protein diet: 0.052%
Yee-ikes, my Swedish lady friends. (Yes, Katarina, I’m talking to you.) Better lay off the “high-protein” foods. Your absolute odds of an ischemic stroke will go up by two one-hundredths of one percent. Oh, and your absolute odds of a hemorrhagic (vessel-bursting) stroke will also go up by one one-thousandth of one percent, according to the study data. Expressed as the relative risk that researchers love to toss around, that’s a 12% increase (0.9 per 10,000 vs. 0.8 per 10,000), so I’d be worried if I were you.
Since the headlines were about the increase in risk for heart disease, let’s look at those numbers. In the high-carb group, there were 8.4 cases of heart disease per 10,000 women. In the high-protein group, there were 12.6 cases per 10,000 women. So expressing the odds as percentages:
High-carb diet: 0.084%
High-protein diet: 0.126%
Even if you accept that the food-recall questionnaires were accurate, that the “high-protein” diet was actually an “Atkins-like” diet (not just people eating a lot of processed meat), and that these figures are actually telling us something about cause and effect (which an observational study cannot do), we’re looking at an absolute difference in the odds of about four one-hundredths of one percent.
In order to stay lean and continue feeling strong and energetic, I’ll roll the dice and take those odds. I have a feeling I can beat them.
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