“Can we finally transcend these diet wars?”
That poignant question, asked by Dr. Kevin Hall, underlined a fascinating debate on the causes of metabolic disease hosted by the American Diabetes Association on the first day of its 80th annual Scientific Sessions.
As three panelists wrestled with the question of what causes metabolic disease, a consensus appeared to emerge that highly processed foods are primarily to blame for the obesity epidemic and the resultant spread of Type 2 diabetes and other metabolic diseases. Neither fat nor carbohydrates alone can explain the rise of metabolic illness in Western society.
The most forceful testimony was given by Dr. Hall, of the NIDDK, who examined the role of caloric excess in the pathogenesis of metabolic disease. Echoing arguments that have been met with some controversy when advanced in previous years by anti-obesity advocates such as Gary Taubes, Dr. Hall dismissed the idea that caloric excess in any way explained the obesity epidemic as a useless truism: “The concept that we are eating too much and burning too few calories is much too simple of an idea.”
“Carlories are important, but that in no way explains what’s going on. It doesn’t explain why people have consumed more calories than they’ve expended. Counting calories does not give you any insights into the cause of Type 2 diabetes… The idea that sometime in the 1970s that not just the US but the entire world lost their willpower to count calories is just nonsense.”
Dr. Hall’s presentation focused on the carbohydrate-insulin model of obesity: the idea that excessive insulin levels due to high carbohydrate consumption essentially act a signal to begin energy storage, causing the fat cells to absorb energy that they do not need, which results in weight gain and in overeating, starting the whole cycle again. This theory has been extremely popular with low-carb advocates, as it tends to blame high dietary carbohydrate consumption for the development of insulin resistance, obesity, and other metabolic dysfunctions.
While Dr. Hall’s research has confirmed some aspects of the carb-insulin model, it has rather pointedly contradicted other aspects. A recent study that he led (available in preprint) randomly assigned participants to either a plant-based high-carb or a high-fat diet, allowing each group to eat as much as they wished every day; after two weeks, the groups swapped diets. Exactly as expected, the participants eating a high-carb diet showed significantly higher insulin and blood glucose levels. However, contrary perhaps to expectations, the people on the low-fat diet ate some 700 calories fewer per day, and as a result lost more weight as well. The results were consistent in every single participant of the study. (The diets were found to be equally satisfying and pleasing, by the way.)
Reviewing macro eating trends in the US since the 70’s, Dr. Hall noted while both carbohydrate and fats have risen in parallel, as a percentage of overall consumption they have remained more or less flat. The most striking change in eating patterns, in fact, has been the explosion of ultra-processed foods, and the concomitant decline in minimally-processed and freshly prepared foods: “If you look at [food] quality in terms of how extensively foods are processed, the consumption of ultra-processed foods has gone up dramatically. It now constitutes more than half of the calories that we consume in many Western nations.”
But most public discussion of highly processed foods (and junk foods) has concentrated on the high salt, sugar and fat contents of these meals. Dr. Hall wondered if this was missing the point, and to test his hunch, he designed a second study. This time, he first put together a two-week menu consisting mostly of ultra-processed meals. With the help of a creative kitchen team, he then designed a second menu of foods that were fresh and minimally processed but that had exactly the same amounts of carbs, fat, protein, sugar and sodium as the first menu. Again, two groups were asked to eat as much or as little they liked of one of the two diets, selected randomly, for two weeks; in the following two weeks, they switched from one diet to the other. Participants on the ultra-processed diet ate an extra 500 calories per day, increasing both carb and fat consumption in concert. They also gained weight. On the less processed diet, the same study participants lost weight.
That there is something unknown but profoundly unhealthy about highly processed ingredients was the focus of the presentation by Dr. Barbara Corkey of the Boston University School of Medicine, a doyenne of diabetes research.
Dr. Corkey emphasized that it is impossible to determine the causation of metabolic disease because we simply don’t know which comes first: insulin resistance, obesity, or hyperinsulinemia. The three states are highly correlated but as yet science has not definitively shown that one causes any other.
“Most people would probably tell me that obesity came first. But I’m not sure that I believe that. And I certainly don’t believe that in the absence of any evidence.”
Noting that many historical communities have thrived on high-carbohydrate diets with no evidence of metabolic disease, Dr. Corkey suggested that the amount of carbohydrates in the modern diet is less concerning than the nature of these carbohydrates. To illustrate her meaning, Dr. Corkey pointed to the ingredient panels on a variety of modern high-carb products, such as Wonder Bread and Rice-A-Roni, which include a bewildering number of additives and chemicals.
Dr. Corkey’s research shows that some of these additives, including monoglycerides and iron, prompt a dramatic increase in basal insulin secretion that is totally unrelated to glucose consumption. Given that Type 2 diabetes and metabolic syndrome are associated with a far greater increase in basal insulin secretion than in postprandial insulin secretion, perhaps these modern additives (that are so ubiquitous in processed foods) have an outsized effect on metabolic dysfunction. She also wondered whether other environmental factors, such as the widespread of use plastic packaging, also contribute to the obesity epidemic in as yet undiscovered ways. Dr. Corkey suggested that much of the success of low-carbohydrate diets may be due to the fact that, by encouraging the consumption of fresh ingredients, they essentially guarantee that dieters will avoid these deleterious aspects of processed foods.
Dr Corkey also agreed with the conclusions of our resident expert, Dr. Mariela Glandt that the use of insulin to treat Type 2 diabetes is problematic. If T2D is caused primarily by Beta cell abuse (by eating a diet that demands more insulin than the pancreas can properly produce), adding more exogenous insulin fails to address the root cause of the condition. The current treatment, which focuses primarily on blood glucose rather than insulin levels, does not lead to a cure, and in fact almost invariably sees the condition worsen over time.
Dr. Sarah Hallberg, the medical director of Virta Health, considered the role of fats in the development of metabolic diseases. “You are not what you eat,” she quipped, reviewing several studies that showed that dietary saturated fat intake was almost wholly unrelated to the amount of saturated fat present in the blood.
Dr. Hallberg demonstrated that body’s use of saturated fat is actually dependent on the context in which it is consumed, the entire dietary matrix, particularly the level of carbohydrate consumption. High levels of carbohydrates tend to raise the insulin response that “shuttles” saturated fat into storage, leading to insulin resistance. But in the context of a low-carbohydrate background, saturated fat is properly used by the body, a healthier outcome.
The message which emerged across all three presentations was that neither fats nor carbohydrates was exclusively to blame for obesity and associated metabolic disorders. Rather, carbohydrates and fats work together, especially in the context of a highly-processed diet, which seems to prompt spiking insulin levels, overeating and weight gain. (Protein, the other macronutrient, escaped blame entirely.)
What does this all mean for the treatment of metabolic disease? Dr. Hallberg asserted that, while humans can tolerate high levels of minimally processed carbohydrates, “Once you have metabolic disease, if you want to control the existing disease, our options shrink to a low-carbohydrate, high-fat intake.”
Dr. Corkey also largely approved of the low-carb approach to metabolic disease, declaring that there was “no valid support for any level of carbohydrate intake in diabetes… You can eliminate carbs without causing harm. You can’t eliminate fats or protein.”
Pointing to a recent study that showed that 88% of American adults have some form of metabolic dysfunction, Dr. Hallberg stated that “most of us right now need to be consuming on the lower-carb, higher-fat end of the spectrum.”
