Harvard School of Public Health epidemiologist Walter Willett talks to SciAm correspondent Cynthia Graber about his latest book, The Fertility Diet as well as about the links between
nutrition and health generally. Plus, we’ll test your knowledge of some recent science in the news.
Podcast Transcription
Steve: Welcome to Science Talk, the weekly podcast of Scientific American for the seven days starting October 15th, 2008. I’m Steve Mirsky. This week on the podcast, Harvard
epidemiologist Walter Willett talks about the connection between diet and fertility as well as other nutrition and health relationships such as the links between diet and cancer. Plus,
we will test your knowledge about some recent science in the news. Walter Willett is the chair of the Department of Nutrition and a professor of epidemiology and nutrition at the
Harvard School of Public Health. His latest book is the Fertility Diet, co-authored by Jorge Chavarro and Patrick Skerrett. Our daily podcast correspondent Cynthia Graber spoke to
Willett.
Graber: You’re known for your research in nutrition and its impact on different health outcomes, and you’ve already written a book about health and nutrition, and I was wondering did
you write a book about fertility?
Willett: Well, this wasn’t a book that I went out to write; this is really based on the work of our Dr. Jorge Chavarro, who is the doctor of students in our department during the last
several years. And this was really Dr. Chavarro’s idea, to look at how diet relates to infertility. We had been studying infertility actually in the Nurses’ Health Study II, [which]
made me to look at oral contraceptives and some other factors that might relate to infertility, and we had also been looking at diet and breast cancer. So Dr. Chavarro was interested in
reproductive health, and he sifted all the data sitting there in the computer – «Why don’t I look at diet and infertility?» And he had some ideas; we knew from the more
extreme case of polycystic ovarian syndrome that this form of infertility – it is strongly related to infertility – is due to insulin resistance, and we had also seen a lot of dietary
factors being related to insulin; so he said logically, he hypothesized that maybe some of those dietary factors that are related to insulin resistance are also related to infertility,
even before you get to polycystic ovarian syndrome. And it turns out that that was confirmed. And then he went on to look at many other aspects by which diet influences fertility.
Various scientific reports have been published over the last two years, and it is scattered in different medical journals. And it occurred to me that this isn’t going to really help
anybody; no individual person even if they are physicians, is going to pull out all of those papers and look at the big picture. So it seemed to me it would really be worthwhile to put
this all together in a way that would be useful to anybody who is interested in being more fertile.
Graber: Can you give me a quick overview of the method of research with the questionnaires and the response[s] of the women, and how many were involved?
Willett: In this study, we had enrolled about a 116,000 women in the Nurses’ Health Study II and we identified about 19,000 who were either trying to get pregnant or did become pregnant
during our follow up here. So we used the diet that they had reported previously and then looked at their subsequent experience regarding fertility. Then in that analysis, we were able
to control for lots of other factors like smoking and other things that might influence their likelihood of becoming fertile.
Graber: How many years was this? Were you following them?
Willett: This was conducted over about a decade of follow-up.
Graber: Could you just give me a quick rundown of what the major recommendations are that the book that you both wrote based on this research, that it encompasses?
Willett: Recommendations can be boiled down to a fairly short list. First of all we are talking about aiming for the fertility window and weight, and that means not too thin and even
towards the lower part of the normal range of weight. Also, we were talking about healthy fats, and that means low transfats and replacing them with healthy liquid vegetable oils. We
are talking about healthy carbohydrates, and that means whole grain, high-fiber carbohydrates and avoiding refined starches and especially sugary beverages; and we are talking about
healthy sources of protein and that means favoring vegetable sources of protein, including some chicken and fish but keeping red meat pretty low. We added a multiple vitamin which has
been shown to improve fertility not just in our study but in other studies as well, and we do add this little interesting twist about low-fat dairy – really staying away from low-fat
dairy while you are trying to become pregnant and adding a serving of whole-fat dairy products per day,. So we put this all together with of course being having [a] moderate level of
physical activity, and it can have an enormous impact on overall chances of becoming pregnant.
Graber: That just seems to be what most people are recommending in terms of diet?
Willett: Right for the most part, what we found is that the general dietary recommendations that we’ve and others have made over the last few years are related to fertility, as well. In
some ways that’s not too surprising. We hadn’t really thought of them as being related to fertility, but your reproductive system has to be healthy along with all the rest of the parts
of your body for good function, and clearly the function of the reproductive part [of] this system is to become fertile.
Graber: So the one part as you know, the one part that might seem more surprising to many people is the idea of having one, at least a serving, of whole milk or full-fat dairy. Can you
explain that?
Willett: Our findings regarding full-fat dairy is [as] being related to better fertility and low-fat dairy being related to less fertility might seem a little surprising; and this is
really the first study to look at this, so they need to be confirmed in other studies before we are completely confident that this is real. But this doesn’t totally come out of the blue
for us, because we have seen a somewhat similar relationship for acne, which we had looked at because we knew that, what we had seen in our data was that a high-fat dairy products were
related to high risk of breast cancer and during the premenopausal years. We were naïve to look at dairy products in relation to acne and we had, again the data was sitting there
in the computer for several different studies. So we put that together and here we found that the low-fat dairy particularly was worse for acne. And what we have learned is, [as] we
have gotten into this, is that the fat part of dairy contains estrogens and progestins. And it’s very possible that those are not bad for acne, for example, because, in fact, we use
oral contraceptives to acne as they are high in estrogens and progestins. And it may well be that those hormones are just giving the developing eggs a little boost and they are giving
them a little added advantage to make it all the way to become functional and allowing a woman to become fertile; whereas the part of the milk that is not fat contains more androgens
and some other growth hormones that may not be so conducive to fertility. That’s [a] hypothesis, so this clearly is a new area that no one has looked into before, and there is a lot
more work to do.
Graber: Speaking of a lot more work to do, you say in the book, you know, at the very beginning, you say that there are millions and millions of dollars that have been spent on
fertility technologies – and certainly many people spend lots of money out of their own pocket to get pregnant – and you also say that little attention has been paid to nutrition; why
is that?
Willett: Well, I am not really sure, but the literature review for this book and for the papers we published wasn’t very easy because there had been almost nothing published on the
relationship between nutrition and fertility. And it’s not totally clear why that was, but clearly there is a huge amount of profit of money to be made in medical technologies for
fertility and that might would have biased the research directions as well.
Graber: I understand that when you started publishing even about cancer that that [the] medical world was also resistant to nutrition at the beginning. Can you just tell me little bit
about that kind of evolution?
Willett: It’s interesting; the ancient physicians actually knew that nutrition was very important, maybe they didn’t have so many drugs around, and they had to live with nutrition. But
they realized it could be important; and if you look at their writings, nutrition gets a lot of emphasis. But in my medical school training, nutrition got almost no emphasis, and it was
even more problematic than that no one really asked the question: Why is somebody getting cancer? Why is somebody getting cataracts? Though We didn’t really think more deeply about the
origins of these diseases, and it was a big wake up when we looked at different parts of the world and found that in many places some of these diseases were very rare that are the most
common causes of death in our country [were very rare]. So I think there’s been a, perhaps a superficiality in our medicine and in our research priorities until very recently, but
during the last couple of decades there has been a much greater recognition that nutrition might be important. When we publish[ed] some of our other findings on diet and cancer, for
example, that alcohol increases breast cancer risk, there was massive disbelief in the medical community even among most of my colleagues; but that has been seen in almost four dozen
studies now, and so that’s very accepted. So a lot of this is just going into new territory that was really unexplored until very recently.
Graber: I read an article this year that was criticizing the method, and I think part of the criticism was that asking people to self-report about their diet and then teasing out a
specific part of diet and the influence is very difficult. What’s your response to that?
Willett: Well, we all know that diet can’t be measured perfectly because every individual probably eats a little bit differently everyday. But our way of assessing diet is, ask a person
about their long-term intake over the past year. So we smoothed out the day-to-day fluctuations [so] that [if] what we eat one day is not [what we eat] the next, [it’s] really not a
critical to us. It’s a long-term dietary pattern of an individual that’s going to be important for most things. And we have done many validation studies where we compared our diet
assessments to biochemical measures, say of, tansfat in the fat tissue of a person or the level of beta-carotene in the blood, and we found pretty good correlations – not perfect but
they are pretty good—and that means that we are able to pick up meaningful differences in people, among people that we can tell someone who is eating a large amount of transfat
from a person eating low amount of transfat. We may not know exactly how many grams a day, but we can put them into groups pretty well.
Graber: And transfatthough – the same way that transfat is shown to be bad for other health outcomes in your book, shows to be – it’s pretty bad for fertility, as well, right?
Willett: We found in our analysis that transfat was related to infertility. It was one of the stronger relationships, and that was actually one of the top original hypotheses, because
we have seen the transfat is related not just to heart disease but also other conditions related to insulin resistance. For example, it’s a risk factor for type 2 diabetes and also
gallbladder disease and so it was not at all surprising that our hypothesis was confirmed and transfat increases the risk of infertility.
Graber: It was interesting to me to read this book after doing my research on acne and the idea that they are both, you know, in large part hormonal changes and responses, and the idea
that food affects the hormones in our body. I just thought that it was fascinating, I mean, just the relationship between the two and the relationship between things that people don’t
necessarily think about and the outcomes.
Willett: The whole area of how our diet and nutrition affects our hormonal levels is quite a new area. A few people have studied this over the years, but there is certainly a lot to be
learned and it is pretty clear though that what we eat in many ways can influence different hormones in the body and that probably does translate into our risk of various diseases, and
in this case infertility.
Graber: You’re right, I think, that one in eight couples are struggling with some sort of infertility; am I correct in that?
Willett: That’s about the right number, yes.
Graber: And do you think that this [these] type[s] of recommendations all gathered in one place, about lifestyle, cutting down on processed foods and sugars and, you know, eating whole
grains, smaller amounts of red meat, omega-3s, getting plant protein, exercise, weight loss, do you think that that can replace some of these expensive fertility treatments? What do you
think the relationship is?
Willett: I am quite sure that for some people a good diet and nutrition can replace infertility treatments; probably not for everybody, but these are so inexpensive and good for health
in general that I think it makes sense for everybody to give a serious try about looking at their diet and activity to become pregnant before jumping into very expensive and treatments
with some side effects as well. Pregnancy is in some ways a challenge that represents some nutritional hurdles, and if you clear those hurdles by better diet and better physical
activity, you are going to be healthier for the rest of your life as well. It’s not simply about becoming pregnant.
Graber: How long have you been doing this type of nutrition research?
Willett: I have been doing some nutrition research really since I was in medical school. When I was in medical school, I spent a summer in an Indian Reservation in the Upper Peninsula
[of] Michigan and went to University of Michigan, and there we did a survey of nutrition and found that half of the population, adult population, was diabetic and that really fascinated
me; and I wondered why, and we also used some dietary assessment methods and found that actually we could learn a lot about what people were eating were some fairly simple ways of
measuring diet; and so in some ways I have spent the rest of my career trying to unravel some of those questions.
Graber: How has your diet changed as you have been doing all this research?
Willett: My diet has changed a lot. I grew up in Michigan and that means roast beef, mashed potatoes and gravy is the right way of eating; and so I had not really experienced many whole
grains, if any. And I have really changed in most ways that I don’t eat much red meat any more, I eat a wide variety of whole grains and vegetables I had not tried before. So my diet is
a lot more interesting and [a] lot more healthy now.
Graber: You mentioned [insulin] a few times in the discussion insulin, and I understand that high glycemic diets, processed foods, sugar etc., leads to insulin spikes. Can you just give
me a quick rundown of how those insulin spikes influence hormones?
Willett: Eating a lot of sugar and refined starches does increase our blood sugar. It really creates some big spikes and large demand for insulin. We are not totally sure how that does
increase our risk of infertility, but we have known for a long time that the more extreme form of insulin resistance that goes along with polycystic ovarian syndrome is related very
strongly to infertility and even now we are not sure exactly how that’s working. So something affecting the basic function and metabolism of cells is saying, «Don’t become
pregnant until you have got your insulin resistance under control».
Graber: If someone who is trying to get pregnant follows the recommendations, how big an effect can something like this have?
Willett: We found that the effect of healthy diet is likely to be very strong of [if] someone who is not following any of these healthy behaviors and then adopts them all, or at least
five of them, it looks like they could drop their risk by about 80 or 90 percent; in other words [it] very strongly favor[s] getting pregnant compared to a bunch of bad dietary
behaviors. If we look at the overall population, it looks like that we could eliminate about 70 or 60 percent of the total cases of infertility that are occurring in the U.S. population
by following these good diet and activity guidelines.
Graber: Does this hold true even for women who are delaying pregnancy?
Willett: That we looked at how this influences pregnancy by a woman’s age, and that’s really important because a lot of women are delaying pregnancy, and we found that that this [these]
dietary patterns related to infertility about the same whether women’s[are] in their 20s or in their 30s; but don’t worry if you’re 65, and follow this diet, you’re not going to get
pregnant.
Graber: One thing I also thought was interesting that I think might surprise people is that you both say that there is little evidence of the negative or positive impact of coffee or
tea, and certainly many people are told to abstain from coffee and tea when they are trying to get pregnant or when they are pregnant.
Willett: The issue of coffee and tea has been inconsistent in the literature; we did not find any adverse effects within the range of coffee and tea that we studied, during which some
women drank quite a bit of coffee. What we found, actually, in other studies is evidence that coffee is decreasing insulin resistance, so it could be that there is some negatives and
some positives with coffee consumption that are balancing each other out, but still we do suggest being modest in your coffee and tea consumption – if you drink, you know, a whole lot
and having [have] trouble becoming pregnant, it just makes common sense to really cut down on it.
Steve: Check out Walter Willett’s Wikipedia entry for links to some additional interviews, including an entire episode of the PBS documentary series Frontline about nutrition and health
featuring comments from Willett; that’s W-I-L-L-E-T-T.