We continue today with the second part of the interview with Dr. Stephan Guyenet (first part here).
In this second part, we ask Dr. Guyenet about some issues that have been discussed in the internet nutrition forums lately, such as the role of insulin in obesity and diabetes, the role that saturated fats play in coronary heart disease, cholesterol or fructose.
- You have had a debate with Gary Taubes about the role that insulin and carbohydrates play in weight control. What is right to wrong about your point of view?
I believe that Taubes has been very useful in the sense that it has introduced many people in the concept of low-carbohydrate diets and publicizing research that questions some of our usual ideas about the health impact of such diets. A number of studies on low-carbohydrate diets have shown that although they are higher in fat and meat, when they are followed by overweight or obese people, they are able to safely cause a reduction in fat as well. as improvements in health during periods that reach two years.
No one really knows what happens after that. They seem to cause more fat loss and perhaps some improvements in metabolism than with more conventional, low-fat diets, in periods of up to a year. However, the ability of low-carbohydrate diets (and other diets in general) to cause fat loss is generally insignificant in most clinical studies. Some individuals respond extremely well to them and lose large amounts of fat. For those people, diet can change their lives.
But nevertheless, Taubes took this useful pinch of information and stretched it too much. He overlooked most of the last 70 years of published research and built a mechanism whereby many of our current diseases, particularly obesity and diabetes, are due to the ability of carbohydrates (particularly refined carbohydrates and sugar) to increase circulating insulin.
It is an extremely simple model if you think about it: hydrates -> insulin acts directly on fat cells -> obesity. In fact, too simple, taking into account the many roles that insulin plays in the various tissues, including the brain, not to mention all the other processes that occur during digestion.
Taubes has criticized very expert researchers for not taking into account his hypothesis, which he considers correct, but which is ignored by researchers for non-scientific reasons (is it necessary to mention here that Taubes has hardly any training or experience in biological sciences ?)
The truth is that researchers have not overlooked their hypothesisThey have verified it in many different ways and have concluded that it is not able to explain obesity. As a scientist, I cannot say with 100% confidence that insulin does not have a certain role in obesity, but what yes I can say with 99.99% confidence is that there are much more convincing explanations that the excess of insulin acting on fat cells is the cause of obesity, and these explanations are those that are being investigated by brilliant scientists.
- Is fructose a problem as Dr. Robert Lustig suggests?
Humans have a long evolutionary past related to fruit. Our ancestors are among the first to eat fruit about 55 million years ago, shortly after its evolution. Mammals probably evolved into primates specifically to access the fruit and our ancestors remained in the trees eating fruits until relatively recently.
Our closest primate relatives chimpanzees get most of their calories from the fruit, and therefore follow a diet high in sugars. All humans who have had access to the fruit have eaten it and enjoyed it regularly.
Studies suggest that the fruit is healthy and may even help weight loss a bit under certain circumstances. But nevertheless, most of the sugar that people consume does not come from fruit, it usually comes from processed corn or sugarcane juice. This is a problem for several reasons:
- The first is that sugar and glucose and fructose syrup they almost completely lack micronutrients and other beneficial substances, and therefore displace other more nutritious meals.
- The second reason is that sugar increases energy density and palatability of food, which leads to eating larger dishes and eating or drinking between meals in the absence of hunger or thirst. This contributes to obesity and the other problems that accompany it.
- The third problem is that yes, in excess refined sugar can cause metabolic problems and these are due to its fructose content. As far as I know, this has only been demonstrated with large amounts of refined sugar or fructose and never with fruits.
Thin people are more resistant to insulin and other metabolic problems that appear with fructose intake, and this is probably related to the energy overload in the liver when there is obesity. It is not clear if the amount of fructose that most people consume today is enough to cause problems. However, I suspect that consuming more fructose on average is a problem. Despite its ability to cause problems when it is in excess, many studies have shown that fructose is not fattening more than other sweet substances with the same amount of calories (such as glucose).
- Is insulin the main problem? What about ghrelin, leptin or other hormones?
The insulin resistance (or the inability of insulin to do its job) is for sure a central problem for health in the 21st century. It contributes to numerous health problems, particularly type II diabetes.
The main cause of insulin resistance is a excess body fatAs simple as that, however, there are many other factors such as exercise or diet quality that also have an impact.
To understand insulin resistance, we have to understand what causes excess body fat. Food intake is regulated by a "symphony" of signals that the brain receives and uses to determine whether a person eats or not. Some of these signals come from sensory organs and the brain itself, while others are circulating hormones that come from the digestive tract, body fat, pancreas and other sites.
This refined system decomposes when a susceptible person is exposed to an abundant amount of very rich and energy dense food, in an environment that minimizes physical activity and sleep, and that promotes psychological stress. The leptin It is a key hormone that restricts food intake, but in this context it cannot do much more. Occasionally, leptin resistance appears, which makes it harder to lose fat once obesity is present.
- Is wheat so bad? If it is, why?
Wheat is surely harmful to about 1% of Europeans and Americans who are celiac. This alone is already a serious health problem that falls mostly on wheat. Beyond that 1%, I suspect there are many other people who can benefit by avoiding it for several reasons, but it is a guess that needs more research to confirm it. There are probably many people who can eat wheat without any problem.
I think that one of the most problematic aspects of wheat is that it is used to make very energy dense products that are also very rich. Flour is a substance that can be mixed homogeneously with fats, sugars, flavorings, creating combinations that are virtually irresistible to the palate. Think of brownies, cookies, cakes or even a hot slice of crusty bread. Most people can find a gap for 200 calories of a chocolate cake even when they are full at the end of a meal. Would a simple cooked potato excite you so much?
A colleague named Matt Lentzer organized something called “A gluten free January”Last year when people left the glute for a month. An epidemiologist named Dr. Janine Jagger and I did questionnaires to get anonymous information from the participants at the end of the month. We found that almost everyone who was overweight lost several kilos, and almost everyone with digestive problems and lack of energy perceived an improvement.
There was no control group, so we do not know what part of the improvement was due to the avoidance of glute, which part was stopped eating junk food and / or the reduction of carbohydrates or how much was due to a placebo effect. However, it does suggest that many people would benefit from neglecting the glute, whatever the mechanism involved.
- What about fats? Why have they been so criticized? What are the real dangerous fats?
Fats are a dense energy source, and saturated fats can increase circulating cholesterol in controlled studies, so it was thought that fats contributed to obesity and the risk of coronary heart disease. I think it is still true that fats can contribute to obesity if it helps increase palatability and energy density in food.
However, paradoxically, fats in the diet are compatible with being able to lose fat in a context of a low carb diet, so there is no such simple relationship. The key, in this context, is that something is being restricted. A combination of many fats with many carbohydrates does not help fat loss.
Saturated fats have received most of the blame for years, but it is increasingly likely that they play a very limited or no role in the incidence of coronary heart disease in humans, in the context of a normal and varied diet.
That does not mean that a person can put a large amount of butter on everything, or that he can drink coconut oil, but in moderation, as part of a varied diet of whole foods, I find no reason to ingest the natural fats present in the card, dairy, eggs or nuts, and to some extent use fats such as butter, unrefined coconut oil, red palm oil, extra virgin olive oil when cooking.
I do not favor refined seed oils ("vegetable oils"). They are refined oils and therefore have hardly any nutritional value, and many of them (for example, from cottonseeds or soybeans) are by-products of other industrial processes.
In addition, they usually have high proportions of polyunsaturated fatty acids and are therefore susceptible to oxidation (which become rancid) when used for cooking. Many of them contain a large amount of omega-6 and very little omega-3, which can potentially alter many processes in the body (although there are exceptions such as rapeseed oil). If you can only use a refined seed oil for cooking, the best is probably the oleic high sunflower oil, a variety raised to be low in polyunsaturated fats and high monosaturated fats.
- Do we have to worry about cholesterol? Can we control it through diet or medication?
Blood cholesterol is contained in particles called lipoproteins. Lipoproteins such as LDL ("bad" cholesterol) and HDL ("good" cholesterol) are causally related to the development of atherosclerosis (hardening and degeneration of the arteries), which increases the risk of heart attack. So yes, I think we should worry about cholesterol. The proportion of total cholesterol and HDL cholesterol is a simple and effective indicator of risk. For those interested, the Framingham risk calculator can give an estimate of the risk of attack in 10 years, with data collected in the Framingham study (//hp2010.nhlbihin.net/atpiii/calculator.asp).
Diet and medications have an impact on lipoproteins. Excess body fat increases LDL and decreases HDL, and fat loss can go around this, to some extent. Polyunsaturated fats lower the level of LDL and HDL. The saturated ones increase both HDL and LDL in test groups of up to three months, but it is not clear to what extent this effect persists in the long term (in any case, it seems that they have no or little impact on the risk of heart attack ).
Dietary cholesterol has a very modest ability to increase LDL and HDL. Moderate alcohol consumption and exercise increases HDL and reduces the risk of heart attack. Smoking lowers the HDL level and greatly increases the risk of attack, although smokeless tobacco does not.
Medications such as statins lower the level of LDL and reduce the risk of attack. These medications have side effects for some people, but they may be worthwhile in individuals with very high risk factors.