Editing Note: This post and the previous post originally were one long article.
In my previous post I explained why nutrition information has a role in the non-diet approach – not as a rule, but as information. But with all the contradictory nutrition advice out there, is there really such a thing as “good nutrition”? There is not one single nutrition principle that isn’t contested by someone somewhere. Doesn’t this mean that there are no reliable facts about nutrition, and everything is subject to reversal?
Actually, no, though it can feel that way at times. While many details of nutrition are speculative, some principles are backed by voluminous research. So how do you separate proven facts from tentative theories presented as facts, or outright misinformation?
Identifying True Nutrition Facts
Misinformation runs rampant in nutrition more than any of field of science. There is so much contradictory advice that most people throw up their hands and decide no one knows anything.
But think about it. Is it really possible that we know enough physics to put a man on the Moon, and we know enough human biology to perform successful brain surgery, and yet we don’t know one reliable fact about nutrition – not even something as basic as whether meat is good for us? Does that make sense?
In nutrition, as in all other areas of science, there are some very well-proven facts that are truly beyond dispute, and then there are theories where the evidence is much thinner. There are two big obstacles to separating out the facts from the theories and misinformation:
- A public information campaign starting in the mid 1970s presented certain untested theories as facts – theories since proven beyond a doubt to be wrong. These include the idea that a high carb, low fat diet is best for health, and that saturated fat and cholesterol is bad for the heart, while polyunsaturated vegetable oils are heart-healthy. In fact, the opposite is true – the evidence is overwhelming. Our current obesity epidemic dates to the dissemination of this bad advice. And yet the misinformation persists because the agencies that disseminated it can’t find a face-saving way to admit their error. (See this previous post for details.)
- Most books and articles about nutrition do not differentiate between what’s known for sure – the facts backed by mountains of evidence – versus recent theories with thin support. So when one of these theories is debunked, people feel like they can’t trust any nutrition advice.
I don’t pay much attention to unproven theories from epidemiological studies. These are the iffy so-called “facts” that are constantly getting reversed. A couple years ago, the New York Times Magazine ran a cover story by Gary Taubes on the problems with epidemiological studies, and why advice from these studies is so often found to be wrong. Epidemiological studies follow large groups of people for long periods of time – what drugs they’re taking, what diseases they get, etc. – and make inferences about what caused what. The inferences are no more than hypotheses – an epidemiological study cannot prove causation – but the news media loves the hypotheses and disseminates them as fact. Worse yet, doctors sometimes act on these unproven hypotheses, to the detriment of public health.
Nor do I pay much attention to findings from controlled studies that haven’t been replicated. There are zillions of these, often extremely narrow in scope. If a study hasn’t been replicated, there is a chance that the finding was random – just a chance outcome. Also, the narrowness of most controlled studies makes generalized conclusions highly questionable. The observed effect may be trivial compared to larger effects that were not part of the study. You can’t draw general conclusions from a narrow controlled study without confirmation from other directions.
But not all nutrition advice is based on flimsy evidence. I do pay attention to nutrition principles that have been proven repeatedly in controlled studies, and especially when cross-confirmed by studies in completely different fields. One example is the indisputable danger to health of a high carb, low fat diet. Evidence comes from countless studies in multiple fields, including endocrinology, biological anthropology, and biochemistry (fat metabolism), along with studies of isolated populations still eating traditional diets. Another example of indisputable fact is the kinds of fats that are good for us (not polyunsaturated vegetable oils). Healthy versus unhealthy fats will be the subject of a future blog post.
Reality Check: Did We Evolve Eating It?
A quick and reliable touchstone for determining whether a so-called nutrition fact makes any sense is by reference to the diet humans evolved eating – the Paleolithic diet. The human genus first appeared on Earth about 2.6 million years ago. This was the start of the Paleolithic Era. From that time until just 10,000 years ago – the start of agriculture and the Neolithic era – all humans lived in hunter-gatherer societies.
The theory of evolution says that our bodies adapt to what is on hand. The individuals whose bodies were best able to use the nutrition from the available food lived to reproduce. Thus the food that was available to human beings for the first 2 million years of their existence is the food that the human body is adapted to eat. It defines good nutrition.
People in hunter-gatherer societies may suffer more frequently from accident and contagious disease, but non-infectious disease – heart disease, diabetes, cancer, colitis, multiple sclerosis, asthma, lupus, etc. – is virtually nonexistent. We know this from studying modern hunter-gatherer societies. The obvious culprit is diet – the new foods we’ve started eating that our bodies are not adapted to use. When hunter-gatherer societies switch from traditional diets to Western diets, they suddenly develop all the non-infectious diseases that afflict our society – diseases previously unknown to them.
While it’s impossible to know exactly what Paleolithic people ate, we can make some good guesses. One way we know is the structure of our digestive tracts, which are very similar to that of dogs and other carnivorous animals, and very dissimilar to that of herbivores (animals that eat only plants).
There is other evidence that we evolved as meat eaters. Fossil remains of large animals like wooly mammoths show marks from stone knives. Plus studies of modern hunter-gatherer societies show that most of their calories come from animal food. From the American Journal of Clinical Nutrition:
Our analysis showed that whenever and wherever it was ecologically possible, hunter-gatherers consumed high amounts (45–65% of energy) of animal food. Most (73%) of the worldwide hunter-gatherer societies derived >50% (56–65% of energy) of their subsistence from animal foods, whereas only 14% of these societies derived >50% (56–65% of energy) of their subsistence from gathered plant foods. This high reliance on animal-based foods coupled with the relatively low carbohydrate content of wild plant foods produces universally characteristic macronutrient consumption ratios in which protein is elevated (19–35% of energy) at the expense of carbohydrates (22–40% of energy).
We also know some practical things. Paleolithic humans did not keep animals – they hunted them. You don’t milk animals you hunt. And we know that until the Neolithic era 10,000 years ago, most people over the age of 3-4 (after weaning) did not have the enzyme to digest lactose, the sugar in milk. Many people today still lack this enzyme, and are lactose intolerant.
One reason that anthropologists think that Paleolithic people did not eat grain is because it was virtually impossible to gather before agriculture, when we specially bred wheat so it would stay on the stalk and be easier to harvest. Also, grain is tiny – it’s just too time-consuming to gather this.
Until very recently, it was thought that humans starting cooking their food only 200,000 years ago, and for most of their evolution ate their food raw. A Harvard anthropologist recently debunked this idea in a fascinating book called Catching Fire. He argues that it was actually the discovery of cooking that allowed our brains to grow so large – that cooking made us human. I thought his argument was very convincing, though some don’t believe it. Many people still use the touchstone of “can you eat it raw” to determine whether Paleolithic people ate it. You can’t eat grain raw; cooking is required to remove toxicity. But even if you allow that Paleolithic people cooked, they probably did not eat grain because of the harvesting difficulty.
In short, here’s what we know: Our ancestors ate the meat of animals they hunted – mammals (herbivores), birds, and fish. They ate eggs only rarely (in spring, when they could find them and climb up to reach them). On rare occasion they’d eat honey, but they had to brave bees to get it. The only milk product they ate was mother’s milk for the first few years of life, and never again after they were weaned. They ate the plants they found growing in the wild – mostly the leaves, fruits, and flowers. They probably only ate roots or seeds in winter when they were desperate since these are harder to harvest and may contain anti-nutrients (cause a belly ache). “Seeds” include grain, beans, and tree nuts – all of these are plant seeds of one kind or another. In particular, they ate little or no grain – the seeds of plants in the grass family. Note that corn is a grain – a corn stalk is a giant stalk of grass. Wild corn was originally a small plant; it’s now big due to agricultural breeding.
Paleolithic people ate plenty of red meat containing saturated fat, but relatively little carbohydrate. Carbohydrate can take the form of starch or sugar, and is mainly found in roots and seeds (the storage parts of plants), sweet fruits, and honey. All but roots are seasonal, honey is dangerous to obtain, and many roots and seeds are toxic raw and difficult to harvest. Paleolithic people did not eat refined or processed food of any kind – no white sugar, white flour, white rice, or vegetable oil. You can’t make any of these things with stone-age technology. If a food can’t be made with a stone knife and a sharp stick (and perhaps fire), they didn’t eat it.
When you evaluate nutrition advice, the general principle is this: Advice that moves you away from what we evolved eating is highly suspect and probably wrong. Advice that moves you closer to what we evolved eating makes common sense and is probably right.
Examples of Bad Advice:
The advice to eat lots of polyunsaturated vegetable oils cannot be right because these were almost nonexistent in the Paleolithic diet, except in the form of whole nuts. (We now know why excessive vegetable oil is so bad for us – more in a future post.) The advice not to eat red meat with its saturated fat and cholesterol makes no sense because we evolved eating plenty of both. The advice to eat a grain-based, high-carb diet makes no sense because we didn’t even eat grain until 10,000 years ago, and no hunter-gatherer society eats a carb-based diet. In fact, dietary carbohydrate is not necessary for life or health. Traditional Inuit (Eskimos) don’t eat any carbs at all since plants don’t grow in the ice, and they are very healthy. The idea that cow’s milk must be a part of any healthy diet does not make sense.
Examples of Good Advice:
The advice to eat less processed food does make sense. Processed food is a very recent addition to our diet, and science has clearly demonstrated many ways in which it harms health. The advice to eat 100% grass-fed beef does make sense, and is important, as we’ll see in my upcoming post about fats. The wild animals eaten by paleolithic people grazed on grass, their natural food.
In general, be suspicious of what Michael Pollan calls “nutritionism”, advice based on the nutritional breakdown of a food rather than the whole food. Avoid weird foods that require advanced technology to produce, no matter what their health claims. Why? Because we don’t know what we don’t know. We can be sure that the Paleolithic diet defines good nutrition, but we can’t reliably list all the micro- and macronutrients that make it so.
Why Nutrition Matters
Beyond the obvious motivation to live a long and healthy life, nutrition matters for this reason:
Not all compulsive eating is emotional eating.
For people whose bodies are sensitive to the quick-digesting carbs we are not adapted to eat (virtually everyone who is overweight), compulsive eating has a physiological component.
Some people can eat a diet high in white flour and white sugar and suffer no obvious ill effects. Others develop unstable blood sugar, carb cravings, and Metabolic Syndrome (obesity, insulin resistance, diabetes). At some point, people in recovery for emotional eating need to address this or they won’t fully reach their goals.
I’m not saying you can never eat another brownie. Nutrition information is just information – it’s not a rule. Not every eating decision has to be based on nutrition. Please don’t try to follow a 100% Paleolithic diet and then pummel yourself when the very thought of not eating grain or sugar makes you crave it.
Just be aware. Notice how refined carbs affect you – both immediately after eating and a few hours later. You may eventually decide you prefer to eat them less often because of how they make you feel.
Thoughts? Comments? I’d love to hear them.