Over the past 20 years there has been an explosion in research on diet and weight management. On the one hand, this is great news since we know more than ever before about diet, nutrition and weight management. On the other hand, a great deal of confusion about the topic remains because quite a few scientists and writers have found evidence that the low-fat orthodoxy that has reigned for over 40 years has some significant flaws. In particular, this orthodoxy has come under sustained and often persuasive attack from authors like Gary Taubes and researchers like Stephen Phinney and Richard Feinman. Of course, scientists fond of the low-fat orthodoxy have shot back with criticism of their own so it isn’t as if the entire field has embraced Taubes’ critique. Because of this back-and-forth debate,it can be difficult to decide on what constitutes a “good diet” or an effective path to weight loss.
In this post, I’d like to give you my sense of the literature and the likely direction of future findings. Just a word of caution: while I am a Ph.D. scientist and widely read in this area, I am not a nutritionist. As a scientist, I have my own ideas about the issues involved but please keep in mind that I cannot tell you what approach makes the most sense for you as an individual – only a nutritionist familiar with your situation can do that. So, with that caveat in mind, let’s cover the big issues being discussed in the field of weight loss and nutrition.
There are three principle types of food: fat, protein, and carbohydrate (fiber is sometimes included as well but isn’t a focus for us yet). These are called the “macronutrients.” While most foods have a mixture of macronutrients it is (very) roughly true that carbohydrates come from grains, starches, fruits and sugars while protein and fats are often found together in meats, milk, eggs and other animal sources as well as nuts and beans. Cooking oils, butter and lard are almost entirely fat. Vegetables are a source of protein and carbohydrates but, because they are typically rich in fiber, they tend to be processed differently from other carbohydrate sources. As a protein source, they are also not “complete.” That is, very few vegetables have all of the types of protein (amino acids) that we need from our diet.
The logic behind “low-fat” dieting is pretty straightforward: fat has twice as many calories per gram as protein or carbohydrate. And since caloric excess is the source of excess fat, it makes sense to cut out the most “fattening” foods when you are trying to lose weight or to avoid weight gain. The idea is that if you can eat the same amount of food but consume fewer calories, then you will still feel full while losing weight.
Interest in low-fat dieting was also driven by a belief, originating in the 1960s, that the consumption of fatty foods filled your arteries with “artery-clogging cholesterol” and led to heart disease. According to this logic, you could reduce weight and promote cardiovascular health by reducing fat intake as low as possible. Dr. Dean Ornish is the leading modern proponent of this theory and his vegetarian diet program has been successful in those that could follow it (more below).
While good in theory, simple caloric restriction by reducing the consumption of fatty food has proven to be mostly disappointing as a weight management strategy. Weight loss diets have been studied extensively and the most common finding is that “dieting” has, at best, a temporary effect on weight. People generally regain whatever weight they lose during a diet. If you have heard the expression “don’t go on a diet, change your lifestyle” then that is why: new ways of eating have to become permanent to induce permanent weight loss.
Later variants of the low fat diet, such as the Mediterranean Diet, were not as strict as the Ornish diet; permitting low-fat meats and seafood, select vegetable fats, and fatty plant foods such as olives and nuts. The typical diet prescribed by a physician or weight loss center has been the Mediterranean Diet or a variant. This diet is generally effective and maintenance is certainly easier than the Ornish diet since it permits a far wider range of foods. Indeed, there is a lot to like about the Mediterranean Diet.
There was always a strong undercurrent of resistance against the low-fat orthodoxy from various quarters. However, it wasn’t until the publication of Gary Taubes’ “Good Calories, Bad Calories” in 2008 that this resistance consolidated and went mainstream. Taubes was influential because he was able to clearly explain – to scientists and lay readers alike – how little of the original low-fat orthodoxy was based in solid science. In particular, he pointed out clear flaws in the original studies that were used to blame fat consumption for heart disease, demonstrated how body fat levels and distribution were clearly related to hormones rather than consumption, and provided copious examples where people living in poverty on a low-fat diet gained massive amounts of body fat.
In Taubes’ view, obesity isn’t explained by a simple over-consumption of calories. Instead, his belief is that “carbohydrate consumption drives an insulin response and insulin drives fat storage.” Of course, you still need to have enough calories in the diet to provide the raw materials for fat storage. Still, the argument goes, it is excessive carbohydrate consumption that drives the process of fat storage. Taubes even demonstrated how animals primed to store fat by hormonal signals will cannibalize their own muscle tissue while sparing fat when starved of food!
This line of attack was especially convincing for a lot of people because the rapid rise of obesity in America corresponds roughly with the release of the USDA Food Pyramid and the widespread promotion of low-fat, high-carbohydrate dietary guidelines.
Is Taubes Right?
The publication of “Good Calories, Bad Calories” and the later (and shorter) “Why We Get Fat” were hugely influential. They not only challenged the prevailing low-fat orthodoxy but led many establishment dietitians start giving people a choice of diets (e.g. Mediterranean or low-carb) rather than being told that one diet fits all people.
Also, Taubes’ work was not produced in a vacuum: prominent scientists such as Harvard’s Walter Willet and Stephen Phinney of the University of California had been following the evidence and questioning orthodoxy for decades. Dr. Willet, chairman of the department of nutrition at the Harvard School of Public Health, was recently quoted in the Los Angeles Times as saying: “Fat is not the problem. If Americans could eliminate sugary beverages, potatoes, white bread, pasta, white rice and sugary snacks, we would wipe out almost all the problems we have with weight and diabetes and other metabolic diseases.” The reputation of Dr. Willet and other prominent scientists gave a lot of organizations in the mainstream reason (and cover) to take a closer look at Taubes’ new ideas.
One of the most compelling research studies to support Taubes was the now-famous A-to-Z Weight Loss Study. In this study, a low-carb, high protein and fat diet (Atkins) was compared with a range of other diets, including the Ornish diet and an orthodox low-fat diet. The result? The Atkins diet was significantly more effective at inducing weight loss than the vegetarian Ornish diet. The results were especially surprising to the study’s lead author, Dr. Christopher Gardner, because he had been a vegetarian for twenty five years.
Next, the medical establishment’s insistence that diets high in fat are dangerous even if they do lead to weight loss simply has not stood up to scientific scrutiny. Indeed, scientists have consistently failed to find any evidence that saturated fat is bad for the heart in otherwise healthy individuals. It may be that plant-based fats are better than animal fats but even that remains a subject of debate. What seems incontrovertible is that replacing saturated fats with carbohydrates is a bad idea. At best, the frequent consumption of red meat may be associated with higher rates of heart disease and cancer but this appears to be due to some factor other than saturated fat (e.g. high levels of heme iron in red meat or the use of growth hormones or corn-based diets when raising factory cattle).
So – that settles it, right?
Not quite: the A to Z study is not without its detractors and there is still the matter of testing Taubes’ hypothesis that carbohydrates stimulate insulin which stimulates fat storage.
Are Carbohydrates Uniquely Fattening?
The first class of studies that have tested Taubes’ ideas are “overfeeding” studies: people are fed well in excess of their needs and their weight gain is tracked. The different study groups are given foods that have different macronutrient ratios. That is, some participants may get a diet high in carbohydrates, while others are fed diets high in fats. Unsurprisingly, lots of extra calories do result in weight gain. More importantly, this weight gain does not appear to be sensitive to macronutrient ratios (high carb diets don’t lead to more weight gain or more bodyfat than other diets). One interesting take-away, though, is that people don’t just gain fat; unless protein is severely restricted, overfeeding leads to more muscle as well as more fat.
The second class of studies are those that measure carbohydrate restriction in the context of normal or calorie-restricted diets. Here, too, the results from varying carbohydrate ratios in tightly controlled feeding studies are not particularly supportive of Taubes’ hypothesis. Participants just don’t seem to lose that much more weight on clinical carb-restricted diets than others on low-fat diets. It is important to note that these controlled feeding studies tend to have very small sample sizes and other methodological problems. Thus, it is too soon to say that the carbohydrate hypothesis is wrong but, to date, the evidence isn’t exactly persuasive.
So what is going on?
Quality of Food May Matter More Than The Carbohydrate Ratio
One of the universal observations of weight loss research is that people do lose weight when they strictly follow a given diet. Of course, when nutritionists design diets they almost always fill it with lots of highly nutritious, mostly unprocessed food. When Dean Ornish designed his ultra low-fat diet, he didn’t just cut out sources of fat, he required participants to consume large quantities of fresh, natural vegetables. He also made sure that participants exercised frequently and practiced stress management techniques such as meditation. Similarly, modern low-carb diets such as Mark Sisson’s Primal Diet don’t just introduce lots of fats and restrict carbohydrates, they emphasize the preparation of meals featuring nutritious vegetables, organically-produced eggs, copious water and full, fatty cuts of (preferably organic) meat. People in the Primal Diet community are also known for attention to lifestyle detail and plentiful exercise.
Despite their differences, all of the diets that have proven effective share in common a requirement that you take time and effort to prepare natural, unprocessed or moderately processed foods and that you consume them in moderate quantities.
This also explains why the results of “feeding studies” are often different from diets that use real food. Feeding studies use a highly processed form of “food” (think gooey-bars) so that they can precisely control both calories and macronutrient ratios. Attempting to achieve precise control of calories and macronutrients using real food – and tailoring it to the food preferences of participants – is impractical. So it may well be that these tightly-designed studies can reveal there to be very little difference between high and low-carb feeding and yet still miss something important about the role of macronutrients.
So Why Do Low-Carb Diets Typically Have An Advantage?
There is no straightforward, scientifically-based answer to this question. However, there are a few things that we can observe that may provide at least the start of an answer. At this point, though, there simply needs to be more research.
First, one thing that all low-carb diets share in common is a lack of “junk” versions of their preferred foods. One can’t easily create a junk-food version of an organic steak or a farm-raised, free range egg. However, low-fat diets have for years featured foods that are not all that dissimilar to highly processed desserts and snack bars.
Second, some scientists have argued that carb-laden meals simply don’t provide the level of long-term satiety as fatty meals. Thus, while a low-fat meal may have fewer calories, this simply translates into a quickly-returning hunger. With hunger being a constant companion, the thinking goes, it is inevitable that people on a low-fat diet eventually fall off the wagon and begin overeating again. People maintaining a calorie deficit on a low-carb (higher fat) diet don’t suffer this constant hunger to the same degree and thus have an advantage.
This is supported by weight-maintenance research that shows that many people who succeed at initial weight loss are left in a near-permanent state of elevated stress: constantly flooded with hormonal signals of starvation even though they are actually at a healthy and sufficient weight. Thus, anything that helps to reduce the influence of this effect should be helpful.
People who are careful about adhering to a low-fat program like the Ornish or Mediterranean diets absolutely can lose weight and can be very healthy. To deal with the persistent hunger that characterizes both weight loss and maintenance, low-fat diets are usually promoted along with inviting pictures of veggie snacks, rice crackers and baked chips to quiet the rumbling stomach. If you make a lifestyle change in which such foods become a satisfying and permanent fixture, you may well succeed. However, it is pretty easy to slide in to the rationalization that a heaping plate of spaghetti or an “energy bar” is acceptable since they are, after all, “low in fat.”
The dynamic isn’t all that different in low-carb and primal eating but there may be a few advantages. First, enhanced satiety is likely to reduce the level of hunger experienced over time. This simply makes it easier to maintain healthy eating habits because the frequency of eating is reduced.
Second, our appetite for a quick bite of left-over steak seems pretty limited and low-carb plans like Mark Sisson’s primal eating or Stephen Phinney’s “art and science” diet have less room for snack food indulgences. The foods that do serve as snacks, such as nuts and “low-carb” bars, are quite satiating in relatively small quantities and not nearly as tasty as, for example, a low-fat pastry. Thus, while you can make a mess of your diet with low-carb eating just as you can with a low-fat diet, the pathways to doing so are marginally less tempting.
So What Do I Do?
Eating well isn’t particularly hard if you simply focus on real foods. In particular, if you elevate fresh vegetables to a “daily must have” you will go a long way toward a healthy diet.
On a personal level, my family’s diet consists of plentiful meat and veggie stews, colorful carbs like sweet potatoes and yams, and near-daily spinach or mixed green salads with extras like grilled chicken, olives, roasted red peppers, feta cheese, and walnuts. Eggs, whole organic milk, real cheese, fish (ceviche!) and cruciferous vegetables play a large role as well. I eat very little bread or wheat but do sometimes wake up to oatmeal or oat-based granola. Is this “optimal”? Hopefully you know by now that a diet that is “optimal” for everyone doesn’t exist. This is the diet that works for me. While I have enjoyed robust good health and low body fat on such a diet, BSDI’s social media head is a strict vegetarian who wouldn’t touch most of the food I eat and yet also enjoys the same robust good health!
Focus on real foods, avoid all processed foods (especially sodas and fruit juices) and then experiment: find the combination of natural, healthy foods that leave you satiated while consuming a modest calorie total and you’ll be on the right path for your healthy lifestyle.