This blog is about the intersection between evolutionary biology and food. But also about practical applications, sustainable agriculture, and general tasty things.
I read an advanced copy of Why Women Need Fat when I was moving and because things were so hectic, I didn't have time to review it before it was released. I haven't heard that much about it though, except for this interesting interview with one of the authors in Salon. It's co-authored by Dr. William D. Lassek and anthropologist Steven Gaulin.
It's an interesting book, but it's slightly hampered by the fact that their theories and prescriptions are both quite complicated and controversial. Unlike most other diet books, the authors are not claiming that their diet will make you thin. In fact, they emphasize the importance of body fat to women and the unique factors that influence women's health risks.
So the book opens up a can of worms because it addresses fat in women, as well as evolutionary psychology. Talk about hot-button topics! But they are indeed strange bedfellows and it's interesting to see the synergy between them both.
The first chapter of the book addresses similar territory as Good Calories, Bad Calories with a history of how dietary fat, particularly saturated fat, became unfairly demonized by Ancel Keys and friends. But there is more discussion regarding the rise of polyunsaturated fats, which were erroneously believed to be a healthy alternative to the naughty animal fats.
Ironically, the next chapter starts with a discussion of Denmark, where women eat more saturated fat than Americans, yet they have lower rates of obesity and heart disease. It's ironic because last year Denmark stupidly started taxing saturated fat to discourage consumption. But here the book diverges a bit from Taubes because they note that actually sugar is a smaller share of calorie consumption in the US than it was in 1961 and overall we eat about the same amount of sugar as the Danes. They also note that the idea that carbohydrates are the culprit also doesn't make sense if you compare countries like Japan to the US.
Instead the authors look towards what they call the single biggest change in the American diet in the past forty years:the enormous increase in vegetable oils high in polyunsaturated fat, particularly the omega-6 variety. We consume more soybean oil than any other country in the world. That's been great for industrial monoculture farmers and food corporations, but hasn't seem to have done much good for our health. To add insult to injury, many of the oils introduced into the diet were not only mostly omega-6 fat, but also were partially hydrogenated, which created trans fats. Trans fats are pretty much unanimous considered extremely detrimental to health even in small amounts (as an aside, on the issue of women and fat, I think it's criminal that the Girl Scouts teach our young women to sell cookies that still contain trans-fats.)
Most food corporations have switched away from trans fats, but polyunsaturated oils are still considered healthy by many, including the USDA. Even people who aren't cooking with the oils are getting generous servings in nearly everything, from salad dressings to baked goods.
But here is where I get skeptical- the authors say that omega-6 could be a cause of weight increases in the population because it's converted into arachidonic acid. But if arachidonic acid is the issue, it makes the later dietary recommendations in the book seem suspicious, because most animal products are rich in arachidonic acid. And many of the studies they cite simply show that people who are overweight have higher blood levels of omega-6, but that doesn't tell us that the omega-6 was the cause. Considering that omega-6 fats are added to almost every processed food, you could blame it on an assortment of things from the palatability of the food (The End of Overeating) to wheat (Wheat Belly). However, it is interesting that it seems that some studies show that the weight gain from those eating diets very high in omega-6 is disproportionately distributed in the waist.
So how do they think this all works? They say that omega-6 makes us heavier by producing certain types of signaling molecules called eicosanoids, which promote the growth and development of fatty tissue and fat storage. Another factor is that such eicosanoids make white blood cells more active, which increases inflammation.
Much like Wheat Belly did with wheat, they also frame their villain as an addictive drug, since the body can make marijuana-like molecules out of arachidonic acid called endocannabinoids. Yes, cannabinoids, like marijuana, and the authors claim that it can stimulate the appetite similarly. But then it goes back to the fact that if this were true, wouldn't other foods rich in arachidonic acid cause similar problems? And those foods include things like meat and eggs.
I think they erroneously dismiss Kressler's book by focusing on sugar, when in reality Kressler also pegged processed fat as a villain as well, just one that works in synergy with other components of processed foods, which seems more likely to be the issue with these omega-6 rich vegetable oils than arachidonic acid.
Either way, through the studies that show omega-6 can cause weight gain disproportionately in the waist seem quite tentative, it is an interesting thing to think about, especially since several chapters focus on the importance of fat distribution.
These are the chapters bring in evolutionary psychology, which discuss controversial theories on the functional attractiveness of the waist-hip-ratio. Anthropologists have surveyed hundreds of cultures across the world and one of the few measures of attractiveness that seems fairly constant is that men seem to prefer a waist to hip ratio between .68 and .72 (even blind men). Does this actually mean anything evolutionarily? Is there an adaptive reason men find this attractive?
Human women are unusual in the first place by how fatty we are. A slim woman can have a body fat percentage of 30%. A chimpanzee female has a body fat percentage around 5%. In this metric, we are closer to whales or polar bears than other primates. The fat is usually concentrated in the buttocks, breasts, thighs, and hips. Studies have shown that the average man finds fat in these areas particularly attractive.
What is this fat for? Interestingly, women tend to lose the fat in these areas as they have children even if they gain weight overall and have plenty to eat. The lose correlates to the number of children a woman has. Lassek and Gaulin found that most of this fat seemed to be lost during nursing. During this period, an average woman eats less than she needs and instead seems to use up this lower body fat.
Why is this happening? It doesn't make sense that women would be just using this fat to give the baby extra calories, because otherwise they would eat more.
Turns out that there is something in this fat tissue that the developing infant brain really needs. The human infant brain is unusually large and it's not just hungry for calories, it's hungry for fat. In particular it's hungry for DHA, the immediately usable form of omega-3 fatty acids that has been found to be crucial for optimal infant brain development.
Unfortunately, the diets of most American women only provide half of the DHA that a pregnant woman and her infant need. Another type of omega-3 fatty acid, Alpha Linoleic Acid (ALA) can be converted to DHA, but this conversion varies (though interestingly pregnant women have upregulated conversion and the placenta also has the ability to push DHA "uphill" creating a higher level of DHA in the infant's blood than in the mother's) and can be down-regulated by excessive omega-6 in the diet.
The authors theorize that towards the end of the pregnancy, a woman eats less in order to foster utilization of her own fat tissues that are rich in DHA. The fat in the hips, buttocks, and thighs has more DHA than the fat in other parts of the body. This DHA has been accumulated over many years, starting in infancy.
I read a frightening Facebook conversation I witnessed in which a girl was bragging about how her thighs didn't touch, another girl mentioned that she was so mad that her thighs kept touching even though she had gotten "thin.". Like this question on Paleohacks, many women find that weight seems to come off everywhere but the thigh/buttock/hip region where the gluteofemoral fat lies. This can be frustrating in a culture where slimness everywhere but the breasts is desired. But seen in the light of the importance of this fat, it makes sense why the body resists mobilizing this fat when weight is lost and many women can't achieve the thinness they want in this region without getting so thin everywhere else that they are dangerously overweight or their ribs are showing. These women don't have "lipodystrophy," they are normal women whose bodies are trying to remain functional in a world where our body ideals have become dysfunctional.
The authors own research that suggests that women with more of this important fat have smarter children.
They also attempt to find a reason why men seem to like small waists, despite the fact that they are associated with low BMI, which is associated with poor fertility. Women aren't just fatter than other apes, we have the riskiest childbirth, a consequences of our infant's oversize brains. The first birth is always the most risky because the birth canal is un-stretched. The authors present data that shows that smaller-waisted women have smaller babies (even though they eat more during pregnancy) and thus easier first-time childbirth. So for most of evolutionary history, it would seem more beneficial for a woman to be neither too heavy, nor too thin, with the fat concentrated in the buttocks, hips, and thighs.
But once the first baby expands the birth canal, a woman can afford to have a bigger baby. And biologically, bigger babies might not be good for a first-time mother, but if they make it out of the birth canal they are more likely to survive and thrive. So the authors theorize that the reason many women find that they are starting to get bigger around the waist after they have their first child is that the extra weight will benefit the next child.
The mechanism they use to explain this is leptin, which plays many important roles in fertility. It also tells a woman's hypothalamus how much body fat she has and then uses this as a guide to tell the body how much of the nutrients that come from meals that she should store and how much should circulate in the blood. When a woman has higher body fat, her hypothalamus "tells her cells to pay less attention to her insulin's request to save." Higher fat stores mean more fat, sugar, and amino acids in the blood. Nutrients are more available to the placenta in the first place and the brain is more amenable to requests for more. But too much fat can be a bad thing at a certain point. Heavier mothers are more likely to suffer from preeclampsia, which could be because the placental hormones that "request" more nutrients are overactive and then the cells of the placenta burrow deeper into the wall of the womb to access the biggest arteries, causing an immune-system reaction. Interestingly, it's more likely if it's the first time a mother is carrying a particular man's child and becomes less likely as she bears more children by the same man.
So Lassek and Gaulin theorize that a larger waist signals to a man that a woman might already have a child to take care of and has also already used up some of her valuable DHA-rich fat. Another controversial idea they introduce is that even a child-less woman will gain weight as she ages because she is likely to have fewer children, so in order to increase the likelihood of genes being passed on, it's more important for any children she has to survive because she might not get another chance. So her waist accumulates fat in order to have a bigger baby, even if that means increasing the risk of the childbirth.
But even if some weight-gain is desirable, things seem to have gone haywire recently. Women gain this weight much earlier and are overall much heavier than their foremothers. They also suggest it's possible that the low amount of DHA in our diets might be responsible for higher overall fat accumulation, reasoning that if a woman gets half as much DHA from her diet as another woman, she will have half as much DHA in each pound of fat. So in order for her body to accumulate an optimum total amount of DHA, she will need to store more fat. I didn't feel the evidence was very strong for this theory, mostly the observation that women are thinner in countries with high-DHA diets, but it is very interesting.
The next part of the book is devoted to the idea of achieving "a natural healthy weight." It examines several studies that show that being slightly overweight (BMI of 25-29) seems to actually be healthy for women (but not for men). A lot of this stuff is similar to what was in the Healthy At Every Size book I read.
Another reason why older women might tend to be overweight, was that in the past this represented a protection against infections like tuberculosis, which killed many thin women. This may be because fat confers more active white blood cells. Luckily, estrogen protects women from some of the downsides of having more fat. Higher estrogen means higher HDL, which is good cholesterol. In general, women are seven times less likely than men to die of coronary disease before age sixty-five (I suspect personally that iron levels play a role here too). There is a downside, in that higher levels of estrogen seem to be related to higher risk of breast cancer, but that seems to mainly hold true for obese, not overweight, women. Overweight women are also more likely to develop type 2 diabetes. The authors recommend that women can follow a high omega-3, low omega-6 diet to help mitigate this risk regardless of a woman's weight.
Some other interesting facts are mentioned, such as the fact that heavier women are less likely to break their hips. Hip breakage is a common cause of death in the elderly. However, heavier women are more likely to have arthritis.
But overall, they say that the focus on heaviness itself is probably misguided, because it's where the fat is distributed that matters. Large waist size in particular seems to be associated with health risks. Interestingly, in the 1990s, about half of women in the overweight group had waist sizes in the unhealthy over-35-inch range. Today roughly three out of four do and 1/7 "normal" weight women also have this problem.
Unfortunately, dieting just doesn't work for most people and in fact people are often worse off after they try diets. Lassek and Gaulin say that calorie restriction makes women miserable and often ends up raising their set points. Instead, they say women should try to return to more human-appropriate diet, with special attention to consuming more omega-3 and less omega-6.
They have a section on reducing omega-6, which mainly focus on fried and processed foods that contain soybean or corn oil. They also recommend being careful about poultry, though weirdly they don't mention pork. They also have a whole section on potatoes as hidden sources of omega-6, but all the potato-foods with high-omega-6 levels are fried or cooked with high omega-6 oils, so it's not actually the potatoes that are the problem.
In order to boost omega-3, they recommend grass-fed meat, wild fish, and/or fish oil/algal DHA supplements. Annoyingly, they don't mention some potential caveats to supplementing such as "fishy burps" and general gastrointestinal upset. It's also definitely not a paleo diet, because they recommend you eat wheat, since it doesn't have much omega-6. They also recommend canola oil, which I personally view with skepticism, particularly if the goal is to return to the diet and thus the weights of our foremothers. I wasn't such a fan of this section of the book. It's clear the authors know much about anthropology and medicine, but not that much about food. I'm glad they are promoting grass-fed meat, but it honestly doesn't have that much DHA. You would have to eat 4.6 lbs of grass-fed beef to get the recommended 1.6 grams of DHA.
And then the rest of the book is about finding your realistic "natural weight," which is the weight your body will gradually shift to once you adjust your diet. This takes into account age and bone structure. Unfortunately, it also involves four steps of calculation. And there are also some eating tips, which are kind of easier said than done:
The interesting thing is that nuts have tons of omega-6. Shouldn't they be bad then? In the end I applaudan approach that recognizes that body fat plays a unique role in women and discourages the eating-disorder-like behavior and unrealism of traditional dieting. Unfortunately, while I think most bloggers I read have a healthy attitude, I see ridiculous bro-science about women's weight like this post on "Top 10 ways to get Skinny Fat." Besides the obvious fact that there are plenty of women who do those things who have ideal or very low body fat, I thought the choice of "scare" picture was telling:
Seriously? That is not a picture of an unhealthy "skinny fat" woman. In fact, there are plenty of women who eat the "magic" paleo diet that many of these sites tout and have much more body fat than that. Not that I think that's a bad thing. Those women are probably much healthier than some of the health bloggers I've seen who are so thin that it really worries me.
That's one limitation to the book. Despite having a more realistic attitude about weight than most books, it still seems to be primarily targeted towards people who want to lose. But the theory the book contains implies that not having DHA-rich fat stores would be bad as well. I personally believe it's possible even for women who are skinny to rebuild healthy curves. I was very very thin when I was raw vegan and over the years of eating fertility-supporting foods like butter and fish roe and improving my digestion I have laid down more fat tissue (and quite a bit of muscle) on my chest, thighs, and buttocks without increasing my waist size very much. I've received similar comments from other women. Is it any surprise that Marilyn Monroe ate a similar diet?
Also, let's get real here. Just like it's absolutely hilarious that writers can quote studies that show foragers are healthy in one breath, and demonize foods that make up most of their diet in another, I think it's weird to tout a very modernized female ideal as part of a "paleo" approach considering that forager women simply don't look like that and that art from the actual Paleolithic seems to portray a culture in which fertility-related fat was venerated.
I also enjoyed the evolutionary theory for the role of body fat in women. But I think their practical advice seems awkward and limited by lack of food expertise. I also think the evidence that omega-6 is responsible for obesity is somewhat limited, as laid out by a recent post by Stephen Guyenet, though I definitely agree that it can cause other problems. And maybe the association only holds up for women?
Some readers have wondered: what's the big deal about these omega-3 fatty acids you have been talking about? So here is a list of important facts and why you should care about them.
Omega-3 fatty acids and omega-6 fatty acids are essential fatty acids that both have important roles to play. The scientific evidence shows that omega-3 fatty acids play an important role in the health of the heart and the brain as discussed in this post from Mark's Daily Apple on Fats.
The standard American diet is very very high in omega-6 fatty acids primarily from vegetable oils and grains and fairly low in omega-3 fatty acids. Why is this bad? From an evolutionary perspective it's inappropriate- we evolved on a diet with a ratio of omega-6 to omega-3 that was 2:1- 1:1. There is strong evidence excess omega–6 intake prevents the body from utilizing omega-3 and even depletes it from our body.
Of course we can have a brain without adequete omega-3s, but for optimal mental development omega-3s play a huge role. This post at Whole Health Source talks about research showing that deficient children suffered various effects ranging from low verbal intelligence to poor social behavior.
In another post he talks about how omega-3s play a huge role in the risk for heart disease.Omega-6s oils are often considered heart-healthy, but this is based on outdated and misinterpreted research. The unfortunate connsquences of a high-omega 6 diet are evident in the Israeli Paradox: people in Israeli consume tons of "heart healthy" oils like soybean oil, yet have very high rates of heart disease.
Seafood is the primary source of omega-3s that are readily utilized by the body. Flax and some other plant sources have small amounts, but their conversion to the usable form is low, though this can be increased by decreasing intake of omega-6 as I discussed in my post about seeds. The most interesting evidence, which Susan Allport talks about in The Queen of Fats, comes from a study that compared Africans eating no fish compared to Minnesotans eating some fish, but also lots of Western high omega-6 foods. The Africans had more optimal omega-3 levels! Their low omega-6 intake allows them to utilize more of the omega-3s found in plants.
The role of the ratio is controversial. Some believe that as long as your ratio of omega-6 to omega-3 is 10:1-1:1, you are in the clear, but Stephen from Whole Health source presented some good evidence that the total amount of omega-6 is more important. His conclusion is that you should get no more than 4% of our calories from omega-6 fats. The sad fact is that eating lots of fish and fish oil might help with preventing heart disease, but it's like putting a bandaid on a severed arm if omega-6 intake continues to be high. Acculturated Inuit still eat plenty of fish, but that so far hasn't protected them from getting obesity and diabetes from consuming too much omega-6.
The bottom line is that omega-3s are important and too much omega-6 is damaging. Ditch the high-omega 6 oils (safflower, sunflower, soybean, corn, canola) and anything with them (store-bought mayo and sauces unfortunately). All the omega-6s you need can be obtained by consuming nuts and fruit oils like olive oil..though not too much of course! It's also probably wise to consume some seafood or fish oil, but the lower the consumption of omega-6s is, the lower that need is. I personally don't take fish oil anymore because it does have some side effects (burping, bleeding more when cut) that I found unpleasant and it's hard to find a fresh and environmentally friendly source.
I hope Stephen from Whole Health Source writes a book about this someday! The only book I can recommend right now is Susan Allport's The Queen of Fats, which is an interesting primer, though unfortunately it focuses too much on the ratio theory.