Is sugar bad? Good? Toxic? What about fat? What causes obesity, diabetes, and heart disease? Does the current state of nutrition science give us answers to these questions?
The answer is a big fat “nope.”
This post has been some time in coming. It is a follow-up, and correction of sorts, to a post I made back in February as part of my series on American health. In the comments section of that post, an enterprising reader noted that most of the available evidence used to set to nutrition guidelines is scientifically unsound. A meta-study from the Mayo Clinic was cited, and I needed some time to go over it in detail and digest its contents. But you can get the gist from the conclusion:
In this critical review, we argued that the essence of science is the ability to discern fact from fiction, and we presented evidence from multiple fields to support the position that the data generated by nutrition epidemiologic surveys and questionnaires are not falsifiable. As such, these data are pseudoscientific and inadmissible in scientific research. Therefore, these protocols and the resultant data should not be used to inform national dietary guidelines or public health policy, and the continued funding of these methods constitutes an unscientific and major misuse of research resources.
The fundamental issue is that most nutrition research depends on having subjects of the study recall, from memory, their eating habits. While various means are used to try to make this accurate, the bottom line is that memory is incredibly unreliable, and does not remotely constitute an empirical record from which sound data can be gleaned. In fact, efforts to methodically replicate previously reported results using more scientific rigor have been unable to do so, demonstrating further that nutritional inventories reconstructed from memory are unscientific.
Unfortunately, memory-based nutrition studies receive a disproportionate amount of funding, and get the bulk of the government’s attention when it comes to setting dietary guidelines. Indeed, the Mayo Clinic report is even more damning:
... despite the important dietary milestones of the past century and the substantial increases in federal funding during the past 2 decades,9,10 research into human nutrition has been increasingly criticized.11,12,13 The genesis of these criticisms is the appalling track record of highly publicized nutrition claims derived from epidemiologic studies (eg, see the studies by Stampfer et al14 and Rimm et al15) that consistently failed to be supported when tested using objective study designs.11,16 Young and Karr examined17 more than 50 nutritional claims from observational studies for a variety of dietary patterns and nutrient supplementation and found that “100% of the observational claims failed to replicate”p117 and that 5 claims were statistically significant “in the opposite direction.”p117 These outcomes and others18,19,20,21 suggest that as often as not, when epidemiologic nutrition claims are tested against objective research methods, the results are either inconclusive or indicative of a contrary outcome.
In addition to these flawed sorts of studies, experiments on mice and rats are also commonly cited as evidence of how various forms of sugar affect humans. Such studies are also of limited use because mice respond to sugar quite differently from humans. For instance, mice easily sicken and die at levels of sugar intake equivalent to what many Americans consume. According to Nature:
High-sugar diets are associated not only with obesity and diabetes, but also with other human conditions such as coronary heart disease. However, the exact causal links for many of these has not been established. When studies are done in mice to evaluate health effects of sugar, the doses given are often so high, and outside the range of equivalent human consumption, that it is hard to tell conclusively whether the results are relevant to people. “Nobody has been able to show adverse effects at human-relevant levels,” says Wayne Potts, an evolutionary biologist at the University of Utah in Salt Lake City.
This does not stop the article from ending with a naked fearmonger by the authors of the study in question:
But Potts and Ruff think that their results are enough to indicate that there is a problem, and that the recommended safe level of dietary sugar should be lowered. “If I show that something hurts mice, do you really want it in your body before we’ve determined whether it’s a mouse-only problem?” asks Potts.
Is too much sugar bad for us? Probably. Too much of anything is bad for you. You can die of water intoxication, or from having too much oxygen in your bloodstream. The old saying goes, “the dose makes the poison.” The problem is, sugars and fats get blamed for myriad health problems and are implicated in millions of deaths when there is, frankly, little sound research to peg them as culprits. To offer one example, the Maasai people of Kenya and Tanzania live on a very high-fat diet consisting mostly of milk, but they are very healthy, likely due to their higher activity levels. One might assume those activities involve intense aerobics and other vigorous exercise, but it’s actually just a lot of walking. Various other cultures have also demonstrated healthy, high-fat lifestyles. What about sugar, then? Cultures throughout Asia have traditionally had high-carbohydrate diets but low rates of obesity and diabetes.
Finding good research that ties all of this together is difficult. The science goes back and forth, alternately blaming sugar, fat, sedentary lifestyles, genetics, and a host of other factors. The search is always on to find the ultimate culprit, the one magic bullet–some food that, if we eat it (or totally avoid it), our health problems will be solved. But the real story is that, overall, we are simply taking in more calories from all sources and we’re moving less than we used to. It’s not about sugar or fat, but how much of everything we eat, and how little activity we get.
The bulk of nutrition science out there, though, seeks to demonize one component of food or another. These days, it’s sugar–sugar is the source of all ill health, and must be stamped out of our diets. In truth, we just need to consume less of it, and less of everything in general, while becoming more active. It also doesn’t seem that we must become dramatically more active, either. Taking up an intense fitness program is probably overkill for most people. But a modest calorie reduction along with a modest increase in physical activity can do a lot of good.
So you can probably ignore the next study that comes out to tell you how bad sugar is for you. Count calories, not sugar.