LET’S ASK MARION: IS THE EVIDENCE AGAINST FAT THIN?

(With a click of her mouse, EatingLiberally’s kat corners Dr. Marion Nestle, NYU professor of nutrition and author of Food Politics and What to Eat:)

Kat: Gary Taubes' new book, “Good Calories, Bad Calories,” presents the hypothesis that carbohydrates, not fat, are to blame for the obesity epidemic, and that the evidence linking a high fat diet to heart disease is unconvincing.

So why the widely held consensus that eating too much fat is bad for us? According to Taubes, it boils down to peer pressure, or a kind of group think phenomenon among nutritionists and scientists who blindly regurgitate the conventional wisdom that excess fat consumption contributes to heart disease. He calls this an “informational cascade,” and credits it with a flood of fallacies about fat’s supposed role in our current health crisis.

Taube’s theory got an approving nod from the New York Times’ resident contrarian John Tierney (aka “the thinking man’s John Stossel”) in Tuesday’s Science Times, but Tierney admits that Taube’s hypothesis remains unproved because the pro-low fat contingent won’t even allow it to be properly studied. Another New York Times science writer, Gina Kolata, began her review of Traube’s book by heralding him as “a brave and bold science journalist,” but concluded it by saying “I’m sorry, but I’m not convinced.”

You described the “Snackwell’s phenomenon” in What to Eat, whereby consumers eat a whole box of high-carb, fat-free cookies because they think “fat-free” equals “low calorie.” The low-fat fad has given rise to all kinds of dubious “innovations,” such as hogs bred so lean that they haven’t got sufficient fat on their backs to be able to survive outdoors. Lost in all this low-fat baloney is the fact that some fats are good for us, and others (such as saturated animal fats) aren't. Do any truly credible scientists dispute that?

It seems to me that most of us are simply eating too much of everything, be it fats or carbs. But I’m not a nutrition professor, just lucky enough to know someone who is. What’s your take on Taube?

Dr. Nestle: Gary Taubes' book arrived while I was in India and I can't comment on it because I haven't had a chance to read it yet. I gather that it comes down hard on carbohydrates. I continue to be impressed by how difficult it is to separate the health effects of fat, carbohydrate, and protein from the calories they provide, the foods that contain them, the diets as a whole, or the rest of the lifestyle that goes along with the diet.

Finding out what people eat is hard to do. Determining the health effects of dietary factors or patterns is even harder to do since humans make such awful experimental animals. Plenty of things about human nutrition are reasonably well established--the basic nutrients that are required and the amounts that prevent deficiency diseases, for example.  But it is much trickier to figure out the effects of nutrients on chronic diseases that are also affected by activity levels, cigarette smoking, alcohol use, and social factors such as poverty, stress, and lack of control. I can't help but be skeptical of journalists who think they have answers to questions that scientists have been grappling with for years.

In a situation in which questions remain, is it better to say nothing or to give the best advice possible based on existing knowledge? Intelligent people may differ on this point but I am convinced that people really want to know what diet is best for their health and want help making food choices. What seems amazing to me is that despite decades of arguments over fat v. carbohydrate, basic dietary advice for preventing chronic diseases hasn't changed in 50 years. I summarize this advice in What to Eat as don't eat too much (eat less, move more); eat plenty of fruits, vegetables, and whole grains; and don't eat too much junk food.

Oh, and the calorie question. It's not that people are overeating 50 to 100 calories a day (the amount in one or two Oreo cookies) and gaining weight. Most bodies can easily compensate for small differences in caloric intake and output. But, as I hear from pediatricians all the time, kids these days are consuming hundreds of calories more than they need, and sometimes thousands. Metabolism--in kids or adults--just can't handle that level of overload. In that situation, carbohydrates may be harder to handle than fats, but both will end up in the body as fat if those calories aren't used up in physical activity.

Fortunately, my precepts leave plenty of room for enjoying delicious food, and aren't we lucky to have so much around.

 

Confusion

There is nothing really new in this book--it is a reprisal of an old idea that gets hauled out every decade or so, and held up as the answer to weight control. The book has a large bibliography, but unfortunately the author omits all the serious recent research that undermines his thesis. For example, he "overlooks" the Weight Loss Registry data of Americans who lost weight and kept it off for a period of a year or more--90 percent of these happy people lost weight--and kept it off--with a LOW FAT diet with exercise. The author actually implies that the French and Japanese, who have the lowest obesity rates in the developed world, eat a low carb diet--when those of us who have worked or lived in those countries know that the French eat white bread at every meal, and the Japanese eat a good deal of white rice. He suggests that exercise is not helpful to weight loss, when there is a huge body of evidence that indicates the opposite. The whole issue of carbohydrates spiking insulin production and therefore fat storage is very appealing to lay people, but it is--to say the least--controversial among experts. Insulin is tightly controlled in the blood stream, and does not "spike" in normal people. All this may explain why not a single endocrinologist or true obesity expert has endorsed this book, while it is wildly praised by low carb advocates and diet docs and folks like Andrew Weil, who shares a publisher--and a love of the spotlight--with this author.

Calories and Fat

I appreciate your noting that calories can come from many sources, and eating far too many is a problem either way. I agree.

I hope after reading Taubes's book you see that is part of the point: eating carbohydrates raises insulin, which is what allows fat to store in the fat cells to begin with (and a variety of other issues). The body perceives carbohydrates as sugar regardless of the source, and the same number of calories in fat/protein vs. carbs does not provoke the same reaction inside the body (at all). Kids are not getting fat because they eat too much chicken and broccoli, but because the vast majority of foods today are heavily laden with carbs, including the grains and starchy veggies and sugary fruits pushed on people as allegedly healthy (not to mention that nearly anything 'fast' whether canned, packaged, or at retail, is junk). We fatten pigs with corn; a vegetable, no less. It is the carbohydrate factor that so effectively contributes to the fattening of pigs -- and people.

As a last note, your comment about a journalist being expert on something scientists have labored for eons on makes sense, but in the detail of this author is not entirely fair.
-- First, every doctor is considered an expert by most folks, yet most doctors have surprisingly little nutritional education (and even less *recent* edu on legit hard science, not just sound bites and overviews in pharma/food-funded medical magazines); this guy probably has vastly more than any doctor I've known, regardless of whether he has a credential to set my broken leg or not.
-- Second, Taubes is not claiming expertise, he is "presenting research" -- legit science by legit scientists -- that the mainstream, in their 20-second sound-byte and driven-by-marketing culture, has completely failed to inform the public about. The book is heavily referenced and any reader has the info as a result to go read research papers and more, and make their own decisions on any topic.
-- Third, I feel that one of the issues in any field is sometimes that people are just too vested in what they 'know' to truly be open to things that challenge their belief systems, in part because it's a threat to their own expertise if it is anything different than what they already believe and promote. I think a truly objective, science minded, good communicator, spending six years heavily delving into the research in these areas, and then writing an intelligent book that pulls it all together for the thinking-layman, is a great thing.

There's more science to be done before anything is known, but the stifling P.C. politics in the field are preventing research and funding (or publicly misrepresenting its findings) that could save millions of lives, not only in longevity but in quality of life. I think his book is long overdue in the world. I'd be interested to hear your thoughts on it when you've had some time to absorb it.

Unabsorbed calories and physiological adaptation

Two important aspects of physiology generate confusion where weight control is concerned. First, the digestive system is not anywhere near 100 percent efficient at absorbing calories. Scientists have measured calorie excretion rates ranging up to 60 percent wastage. Consequently, no laws of thermodynamics are broken when people increase caloric intake but don't gain weight.

Second, the body adapts to variations in timing and amount of caloric intake by remodeling the digestive system or altering tissue. For example, rats fed once a day will often develop larger stomach capacity and increased intestinal absorption area.

Another adaptation has to do with brown fat tissue. Brown fat is metabolically active fat tissue that is rich in blood vessels. It burns fat generating heat to help regulate body temperature. Slender people often have more brown fat tissue than the obese whose bodies are somewhat insulated against heat loss.

These are but a few of the physiological differences between individuals, differences that predict how many calories get utilized and how much energy is wasted.

David Brown
Nutrition Education Project

It's calories, and I believe it

I'm in the low-cal, not low-carb, camp. I'd be wither away without my carbohydrates, and this recent study backs me up! I say, bring on the potatoes and pasta!