Saturated Fat Study

You may have seen news stories earlier this week about a study showing no statistically significant effect of saturated fat intake and fatty acid supplements on heart disease. I have several things to say about this; I will start with the executive summary, if you trust me and want some quick advice, and then move on to some notes about how to approach news articles and scientific papers.

Main Lesson

The main thing you should know is that this study provides more support for the general nutritional rule that focusing on one particular thing is usually a mistake and supplements are probably not helpful.

Good nutrition means eating as many calories as you burn, and making sure that you get all your essential vitamins, minerals, and amino acids. If you are eating too much, then eating too much saturated fat is not noticeably worse for your heart than eating too much of other things. If you are eating the right amount and getting your micro-nutrients, than foods high in saturated fat can be a healthy part of that diet.

However, trans fat is an exception; people who ate more trans fat were 16% more likely to have coronary disease. The fact that this was the only type of fat that caused a significant change is a big deal, and almost no news articles mentioned it. Of course, correlation is not causation. We do not know for sure that trans fat itself is what caused the problem; it could be that trans fat consumption is mainly a symptom of eating a lot of processed foods and restaurant food. 

Reading Health News

Whenever you see this kind of news story, remember that one study is just one bit of information added to a giant pile. A meta-analysis like this one is best seen as one team's report on how they searched through a giant pile of data.

Also, you should be suspicious of any news article or blog post that does not link directly to the actual scientific article, like I did. There is no excuse for not doing this. Even if the actual article is behind a paywall, you can almost always see the abstract for free. 

Most of what I am saying about this study is stuff you can read for yourself in the abstract. Yes, the language they use is often arcane and intimidating, but it does not take long to learn how to read medical studies, and the benefits of doing so are substantial.

Reading Scientific Papers

This study did not show that eating more red meat or saturated fat would be harmless. Here is what it found (the quote is directly from the abstract, edited for clarity):

"In observational studies, relative risks for coronary disease were 1.02 (95% CI, 0.97 to 1.07) for saturated...fatty acids when the top and bottom thirds of baseline dietary fatty acid intake were compared."

This is saying that they looked at people, ranked them according to how much saturated fat they ate, and divided them into three buckets: the bottom third, the middle third, and the top third. They then compared the amounts of coronary disease among the top-third bucket and the bottom-third bucket. The people in the top-third bucket had 1.02 times as much coronary disease.

This number of 1.02 had a 'margin of error' of plus or minus 0.05, which means that it could be as low as 0.97 or as high as 1.07. So while the 'best guess' is that the people who ate more saturated fat were 2% more likely to have coronary disease, this number is not known with enough precision to say for sure that the difference is real.

Notice that they did not feed saturated fats to people and see what happened. They simply looked at a population and reported correlations between saturated fat consumption and heart attacks. They did not find a very strong correlation. But remember that absence of evidence is not evidence of absence. The fact that this study did not find a 'smoking gun' does not mean that saturated fat is harmless. And also note that they did not look at longevity or any other health outcome. 

It is always a mistake to read too much into one paper; science is about learning lots of little facts, but people seem to have an instinct to make grand sweeping claims on the basis of a few little facts.

Still, this is useful information, because it tells us that saturated fat is not necessarily a major villain that we should be obsessed with. Eating too much saturated fat should be seen as one of many possible ways to eat badly, one that is not noticeably worse than the others.

Now, compare the results for trans fats:

"In observational studies, relative risks for coronary disease were ... 1.16 (CI, 1.06 to 1.27) for trans fatty acids when the top and bottom thirds of baseline dietary fatty acid intake were compared."

This is a significant finding. People in the top-third trans fat bucket had 1.16 times as much coronary disease than people in the bottom-third bucket. People who ate more trans fat were 16% more likely to have heart attacks than people who ate less, although that number could be as low as 6% and as high as 27%.

If all I know about you is that your intake of trans fats is in the top third of the population, than your risk of heart disease is 8% higher than the average person's. If all I know about you is that your intake of trans fats is in the bottom third of the population, than your risk of heart disease is 8% lower than the average person's.

Again, this was not a controlled experiment. They did not feed people trans fat to see what happened. This does not definitively say that trans fat will cause heart attacks. It says that people who eat foods with more trans fats are more likely to have heart attacks. It is possible (but unlikely) that something else about the food with lots of trans fats is the real culprit.

But in any case, we know that the kinds of foods that have historically been high in trans fat are correlated with more heart disease. It is probably the trans fat doing the damage, but it could be something else. Either way, this study provides evidence that it is a good idea to avoid trans fats and they foods that contain them.

Required Calories

My food consumption yesterday would have been very healthy for most people. Breakfast and lunch were footlong subs at 700 calories each, and for supper we went to a sit-down restaurant. I had soup, a catfish entree, and bread pudding, but the portions were fairly small so the meal was probably less than 900 calories. So overall, I ate lots of vegetables and lean protein and some whole grains, with total calories less than 2300.

This morning I felt a little out of sorts and my gut ached a bit. I was worried that I had eaten something bad. I did not think it was hunger, because when I thought about getting another sub sandwich my body vetoed it with a feeling of disgust. When I got to the airport and got through security, I started looking around for breakfast. I saw a McDonalds and decided I wanted to eat there. I saw the big breakfast and immediately realized that I really wanted 1300 deliciously empty calories for only $5.

When I got the food, I devoured it like a famished hyena, and then immediately started feeling much better. I realized that has not eaten enough calories yesterday to fuel myself. My body had been telling me that 2300 calories just was not enough to do what I asked of it, such as always taking eight flights of stairs up to my hotel room rather than take the elevator like a normal person. The feeling of not wanting to eat a sub was my body telling me not to waste stomach space with low calorie food when I needed fuel.

Until about 100 years ago, good nutrition meant getting enough fat, carbs, and protein to keep one functioning. For those of us who are physically active, sometimes it still is.

Sugar Limit

We are seeing more and more recommendations to cut sugar consumption. This is probably good advice for most people, but it is important to keep a sense of perspective.

Nutrition advice tends to go through fads, and these fads rarely have strong evidence behind them. We cannot do proper random trials on the macronutrient (fat, sugar, protein) mix of human diets for ethical reasons, and there is rarely even any good observational data that you can base strong conclusions on. So people are left to guess based on animal testing and metabolic models.

Back in the 80's, fats were demonized. Food manufacturers responded by making 'low fat' foods with lots of added sugars. Now it is the added sugars that are taking the blame for obesity. It is true that sugary foods with few micronutrients (vitamins, minerals, amino acids) do bad things to your body in excess, just like fatty foods with few micronutrients.

I eat a very healthy diet; I almost never eat restaurant or processed foods and I eat lots of fruit, vegetables, and whole grains. Yesterday was a fairly typical food day for me; the only added sugar I ate came from half a loaf of my homemade bread. I use 2 tablespoons a loaf, so I would have eaten 1 tablespoon, or 12 grams of added sugar, which is well under the WHO's new suggested limit.

But I also ate three apples and a pound of strawberries, which according to Wolfram Alpha contains 79 grams of sugar. So theoretically I am way over the limit, but I find it highly unlikely that eating three apples and a pound of strawberries for lunch is a bad idea.

Biologically, there is no difference between added sugar and sugar in fruit. Fructose is fructose. The fruit gives me lots of vitamins and fiber, of course, but that is the only thing that makes it better.

I believe that the only two nutrition rules that really matter are to eat as many calories as you burn, and make sure you have enough vitamins, minerals, and amino acids. The more you exercise, the easier it is to follow these two key rules, and of course exercise is very good anyway.

Rules like ‘keep sugar under 5%’ are probably just fads. Beware any nutrition advice that makes absolute claims or blames a particular food item or macronutrient for all of your problems.

Food Regulation Cost Benefit Analysis

The basic process of cost-benefit analysis is to think about all of the main effects and side effects of the regulation, and figure out how to put a dollar value on them all so we can compare everything and make sure we are doing more good than harm.

Valuing life and health in dollars sometimes sounds wrong to people, but it has to be done in order to govern intelligently and there is a large and well-researched literature showing how to do it right.

When a regulatory agency passes a regulation that costs money, that makes people poorer (and possibly unemployed). They react by eating less healthy foods, living in more dangerous areas, buying less safe products, working in harder and more dangerous jobs, etc. The value of a statistical life is about $10 million. That means if we pass a regulation that costs $10 million, we are basically killing someone, so we need to make sure that we are saving a life to make up for it.

Of course, quality of life matters as well. If we make enough people live longer and/or healthier lives, it is as good as saving a life. The measurement that is used to tie everything together is a year of healthy life. Giving someone a year of healthy life is valued at about $200,000. We count up the number of years of healthy life that the regulation will give to people, both by preventing premature death and improving their quality of life, and multiply that by $200,000 to find the dollar benefits of the rule.

We could count all of the costs and benefits in years of healthy life, and in a sense we are, but using dollars as the metric makes things easier.

Doing an analysis of food regulation follows the same basic process as any cost-benefit analysis. The only difference is the detailed knowledge of what to measure and how to measure it. We keep data on how many years of healthy life are typically lost due to various kinds of food-related illnesses and disease, and we have data on the size of the food industry and how much it would cost for them to respond to various types of regulation. 

The data is never as good as we would like, of course, and sometimes we have to scramble for estimates of something that we do not know about. The important thing is to make sure that nothing big is being left out, and that we have the right order of magnitude for everything we do measure.

Obesity Article

Here is a long but very good and sensible article on obesity, with an emphasis on social realities, effective change, and not making ideals the enemy of marginal improvements:

 http://www.theatlantic.com/magazine/archive/2013/07/how-junk-food-can-end-obesity/309396/?single_page=true

The author makes a few annoying mistakes, like assuming that vitamins in supplements are as good as those in actual food, and downplaying the fact that two foods with the same calorie count can have very different health profiles, but there are a lot of very good points.

It is still true that, holding all else equal, it is best to avoid processed food. But it is important to remember that a processed food with a good health profile (low calories, low salt, low fat and added sugar) can indeed be much healthier than a natural food or homemade recipe that is loaded with fat and sugar.

Precautionary Principle

The precautionary principle is the idea that new things should be forbidden until they are proven to be safe. It is opposed to our traditions of freedom, which say that people are innocent until proven guilty and should be allowed to do what they want unless the state can prove that they are harming others. It is also opposed to cost-benefit analysis, which says that things should only be forbidden if the likely harm is greater than the likely benefits.

The precautionary principle is closely tied to the human instincts of repugnance and disgust. People are far more likely to apply it to things that seem 'wrong' or 'bad'. Once something flips a mental switch, people enter a new mode of thinking where tolerance disappears and they become extremely conservative and suspicious. Rather than thinking about the new thing in a balanced way, they decide that the new thing is bad and demand impossible proof that it is harmless.

People are especially likely to apply the precautionary principle to food. There are good evolutionary reasons for this. The natural world is full of toxic substances that will kill or sicken someone who eats them. People who ate everything without question were less likely to pass on their genes than people who waited to make sure that the thing was safe before eating it.

Like many instinctive behaviors, the precautionary principle leads to bad results in the modern world. The benefits of modern civilization that have allowed us to escape from the nasty, brutish, and short lives of our ancestors come from scientific innovation. The precautionary principle makes this innovation much harder. Most of the good things of civilization have some kind of associated harm. Sometimes the harm is small, and sometimes the harm is significant, but it is usually much smaller than the benefits. If our ancestors had applied the precautionary principle to every innovation, we would still be in the dark ages.

Sometimes the benefits are hard to see, and the harms are obvious. For example, agricultural chemicals make fresh vegetables cheaper, which allows more people to eat vegetables more often, which improves the diet and delivers small health benefits to large numbers of people. However, those same chemicals cause some people to get cancer. The health benefits from the cheaper vegetables are several orders of magnitude larger than the harm done by the cancer, but the cancer is much more visible, so people pay more attention to it.

The tools of science can give us good estimates of how much harm something is likely to cause. Because all good science deals with probabilities and not certainties, it is impossible to prove that something will have zero harm. Even if we predict some harm, we may also predict that the benefits are likely to be much larger than the harm. In both of these situations, a scientific cost-benefit analysis will say to do something, while the precautionary principle will say not to.

However, the precautionary principle makes better stories and narratives than science, because it is closer to human instincts. It feels more moral for people to apply the precautionary principle than to crunch numbers. Often, these feelings are what drive policy. People trust their instincts instead of the scientific method, and stop or delay new technologies. The end result of this is that we are stuck with old and inefficient ways of doing things, wasting valuable resources that could be used to improve our lives and our society.

Naturalistic Fallacy

The naturalistic fallacy, or the appeal to nature, is the belief that natural things must be good and unnatural things must be bad. This belief causes a lot of problems in the food market.

A big problem comes from the fact that the word 'natural' has no real meaning or definition. It is just a vague fuzzy concept that is different for everybody. This means that advertisers and marketers can use the word to mean almost anything they want. A recent court decision threw out a case where a company was being sued for using high fructose corn syrup in a product and calling it 'all-natural'. I personally would consider corn syrup to be a synthetic substance, because it comes from a factory, but the court ruled otherwise.

This is a good object lesson. There are a lot of words like 'natural', 'fresh', 'fair', and 'healthy' that sound good but are hard to define in terms of numbers or logic or things that can be measured in a lab. When you see someone using those words, you should assume that they are trying to manipulate you.

In fact, a good rule to follow is to never trust anything on a food package outside the nutrition facts panel. There are a few rules about what can and cannot be said, but they are fairly easy to slither around. On the rare occasions when I buy packaged foods, I only look at the ingredients and nutrients in the nutrition facts panel and consider everything else on the package to be meaningless noise.

But even if the word 'natural' had a clear legal definition that was consistently enforced, it would not be a good guide to healthy eating. Lots of natural things, like slabs of organic red meat loaded with saturated fats, are not healthy and should only be eaten in moderation if at all. Lots of unnatural things, like iodine in salt, are public health miracles that save billions of people from nasty diseases.

It is true that chemical factories produce a lot of substances not found in nature. But it is not true that our body is helpless to deal with these things. In nature, plants are in a constant state of chemical warfare with the things that want to eat them. Humans have an amazing ability to detoxify these poisons. We can eat and enjoy things like chocolate that are full of chemicals that can kill other mammals like cats and dogs. The detox systems of our bodies can usually deal with nasty artificial chemicals the same way they deal with nasty natural chemicals.

For example, we now know that even the detox systems of a fetus can render harmless the amounts of BPA found in our food. If you do not know what BPA is, then you do not need to. If you have read or heard that it is harmful, than you can stop worrying.

Our instincts want to classify everything as bad or good, and then to completely avoid bad things while seeking more of the good things. The naturalistic fallacy is a subset of that problem. The world does not work like that. The dose makes the poison. Essential vitamins can kill you in large doses. Nasty chemicals are harmless at small doses. As in many things, moderation is the key.

Now, however, I should point out that many of the fundamental rules for a healthy diet are similar to the naturalistic fallacy. You should limit your consumption of packaged food and eat lots of raw agricultural commodities. You should avoid eating things like refined sugar in quantities larger than the human body evolved to handle. You should remember that many important nutrients like calcium will only help you if you eat them in food, and that dietary supplements with those same nutrients are worthless or even harmful because the nutrient is in an unnatural form that the body cannot absorb properly.

As usual, the conclusion is to avoid simplistic thinking about the world, and consider the science and evidence. Understanding the sciences of biology and chemistry and psychology will allow you to make good decisions about things you have not seen before, while relying on simple intuitions or trying to memorize a list of good and bad things will not lead to good results.