Hello and welcome to Nutrition Facts – the podcast that brings you the latest in evidence-based nutrition research. I’m your host, Dr. Michael Greger.
I’m often asked what my opinion is about one food or another. I know what people are asking but, you know, I’m not interested in opinions. I’m not interested in beliefs. I’m interested in the science. What does the best available balance of evidence published in the peer-reviewed medical literature show right now? That’s why I wrote my book, “How Not to Die”, and why I created my nonprofit site NutritionFacts.org and, now, this podcast.
Today, we’re going to discuss men’s health and, while we know men and women have many of the same health issues, there are important ways in which they diverge. Take infertility in men, for example. It appears that dioxins, endocrine-disrupting pollutants, heavy metals, saturated fat, and steroids in the meat supply may be affecting sperm counts, semen quality, and the ability of men to conceive. Here are the details of some of those studies.
Infertility affects 10 to 15% of couples attempting to conceive and, in about half the cases, a problem is found in the man. A recent Harvard study found that increasing saturated fat intake just 5% was associated with a 38% lower sperm count, but why? I’ve talked about the role of xenoestrogens, endocrine-disrupting industrial pollutants that build up in animal fat, particularly fish, but male fertility is not just about sperm count, the number of sperm, but about how well the sperm themselves work.
A recent study found that successful pregnancy and fertilized egg implantation outcomes are decreased in patients reporting a more frequent intake of meat. This finding is consistent with poor semen quality associated with a higher intake of products that may incorporate these chemicals and steroids. The use of these compounds in the food industry results in an increased total level of xenoestrogens and sex steroids in processed foods, such as meat or milk, whose intake contributes significantly to daily exposures. Xenoestrogens are highly lipophilic substances that can accumulate in fat-rich foods, such as meat, and may be suspected as partially responsible for the decline in semen quality. Conclusion: Couples having trouble conceiving must be advised about the drastic effect of both the male and female lifestyles on infertility treatment success.
This is consistent with previous findings that frequent intake of fat-laden foods, like in meat products and milk, may negatively affect semen quality in humans, whereas some fruits or vegetables may maintain or improve semen quality. Vegetable consumption was also found protective in the new study, which may be because of the antioxidant and nutrient content of these plant foods.
The adverse effects of meat could be from other pollutants as well. Exposure, even as an infant, to low levels of dioxin can permanently reduce sperm quality. The general consensus is that human sperm quality has declined over time in different areas. We’re still not sure why, but dioxins may be playing a causal role.
The reason why maternal beef consumption may alter a man’s testicular development and adversely affect his future reproductive capacity is thought to be due to the anabolic steroids implanted into the animals. But, as the accompanying editorial points out, the steroids could also be interacting with other xenobiotic (meaning industrial chemicals) present in meat, such as pesticides and dioxin-like pollutants, and even chemicals that may be present in the plastic wrap.
Heavy metals may also play a role. Lead and cadmium exposure, as measured in the bloodstream, was associated with a significantly longer time to conceive. Where might exposure be coming from? Well, common types of seafood, right out of fish markets and supermarkets, were sampled. The highest cadmium levels were found in tuna, highest lead levels found in scallops and shrimp. The greatest risk from different metals resided in different fish, some of which got really high. Thus, the risk information given to the public (and mainly about mercury) does not present a complete picture. There are other toxic metals in fish as well.
The largest and oldest fish had some of the highest levels and we see that with other animals, as well. For example, contamination of beef by cadmium and lead, clearly dependent on the age of the animal.
The only beverage associated with infertility in women was soft drinks, though this may be from an indirect route, with soda linked to obesity, and then obesity then linked to reduced fertilization rates. Though there has been a study on one really direct route, The Effectiveness of Coca Cola as a Spermicidal Agent in Vaginal Douching; Diet Coke apparently had the strongest effect, Harvard researchers publishing in the New England Journal of Medicine.
What about Coke versus Pepsi? Taxpayer money hard at work for this head-to-head test and neither of them really worked, Coke nor Pepsi, though they explain their methods for preparing the sperm-cola mixtures differed from the Harvard group. Bottom line: Soda probably isn’t good for you going into any orifice.
It also appears that endocrine-disrupting chemicals have been found in the aquatic food chain and that they may affect genital development and sexual function in men. Here’s more.
A number of studies suggest that exposure to industrial pollutants may affect sexual function, for example, loss of libido, sexual dysfunction, and impotence. This may be due to effects on testosterone levels. In a study of men who ate a lot of contaminated fish, an elevation in PCB levels in the blood was associated with a lower concentration of testosterone in their blood.
Testosterone doesn’t just play a role in determination of secondary sexual characteristics, like facial hair at puberty, but in normal sexual functioning, and in overall physical and psychologic wellbeing in adult men. Abnormally low levels of testosterone can lead to decreased physical endurance and memory capacity, loss of libido, drop in sperm count, loss of bone density, obesity, and depression.
These so-called endocrine-disrupting compounds that build up in fish may be able to mimic or block hormone receptors or alter rates of synthesis or breakdown of the sex steroid hormones. In children, these pollutants may actually impair sexual development. Boys who were exposed may grow up with smaller penises, though we’re only talking about two-thirds of an inch, at most. We’re not sure if the effects on penis length are due to the proestrogenic effects of the toxins or the antitestosterone effects.
In fact, if you expose cells from aborted fetal human penises to these kinds of dietary pollutants, gene expression related to genital development is affected even at real-life exposure levels. These toxins are found predominantly in fish, but also meat and dairy, with the lowest levels in plants.
You’ve heard of save the whales? Well, male reproductive organs may be at risk from environmental hazards.
When it comes to prostate cancer, it appears that reducing the ratio of animal to plant protein in men’s diets may slow the progression of the disease.
It is now eight years since the famous Ornish study was published, suggesting that 12 months on a strictly plant-based diet could reverse the progression of prostate cancer.
Wait a second. How were they able to get a group of older men to go vegan for a year? They home-delivered prepared meals to their door, figuring men are so lazy they’ll just eat whatever is put in front of them.
But, what about out in the real world? Realizing you can’t even get most men with cancer to eat a measly five servings of fruits and veggies, researchers settled on just trying to change their A:V ratio (the ratio of animal to vegetable proteins) and, indeed, were successful in cutting this ratio in half, at least, from about 2:1 animal to plant, to kinda half-vegan, 1:1.
How’d they do? Looks like their cancer was slowed down. The average PSA doubling time, an estimate of how fast the tumor may be doubling in size, in the half-vegan group slowed from 21 months to 58 months. So, the cancer kept growing, but with a part-time plant-based diet, they appeared to be able to slow down the tumor’s expansion. What Ornish got, though, was an apparent reversal in cancer growth. The PSA didn’t just rise slower, it trended down, which could be an indication of tumor shrinkage. So, the ideal A:V ratio may be closer to zero.
If there’s just no way grandpa’s going vegan and we just have half-measures, what might be the worst A and the best V? Eggs and poultry may be the worst, respectively doubling, and potentially quadrupling, the risk of cancer progression in this study, out of Harvard. Twice the risk, eating less than a single egg a day; quadruple the risk, eating less than a single serving of chicken or turkey.
And, if you could only add one thing to your diet? Cruciferous vegetables. Less than a single serving a day of either broccoli or Brussels sprouts, cabbage, cauliflower, or kale may cut the risk of cancer progression more than half, defined as cancer coming back, spreading to the bone, or death.
This animal-to-plant ratio might be useful for cancer prevention, as well. For example, in the largest study ever performed on diet and bladder cancer, just a 3% increase in the consumption of animal protein was associated with a 15% higher risk of bladder cancer, whereas a 2% increase in plant protein intake was associated with a 23% lower risk. Even little changes in our diet can have significant effects.
And now it’s time for some information you may find surprising and it has to do with watermelons.
As noted in a recent article in the Harvard Health Letter, up to three-quarters of men with cholesterol-narrowed coronary arteries have some degree of erectile dysfunction as well. There’s drugs like Viagra, but they’re a temporary and an expensive solution that can cause hazardous side effects.
Obviously, if your arterial system is that damaged, a more intensive effort that involves much more than popping a pill can yield longer-term improvements in both sexual function and cardiovascular health. Plant-based diets can not only reverse both conditions, but one plant in particular may be able to play a stopgap role in the meantime.
The way drugs like Viagra work is by inhibiting an enzyme that inactivates something called cGMP, which would otherwise dilate penile blood vessels. So, enzyme inhibition means more cGMP, which means more blood flow.
But there’s another way to boost cGMP levels, by going to the other side of the equation and stimulating the enzyme that makes it. That’s what nitric oxide does. Nitric oxide is made from arginine. Arginine can be produced by citrulline. So, I wonder what would happen if you ate more citrulline. Oral citrulline supplementation improves erection hardness in men with mild erectile dysfunction.
And where is citrulline found? Watermelon. How much watermelon would you have to eat every day to match the dose they used in the study? Three and a half servings a day, unless you eat yellow watermelon, which has about four times as much citrulline. So, just one serving a day, one wedge, one-sixteenth of a modest melon should provide the dose they used, allowing for a 68% increase in monthly intercourse frequency, which your heart should be able to handle, given how much lower your blood pressure will be with watermelon supplementation. Watermelon’s got it all!
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Thanks for listening to Nutrition Facts. I’m Dr. Michael Greger.