How Plant-Based Diets May Extend Our Lives
A recent review suggested that plant-based diets may prove to be a useful nutritional strategy for lifespan extension in part because they tend to be naturally low in the amino acid methionine (see my video Starving Cancer with Methionine Restriction). Apparently, the less methionine there is in body tissues, the longer different animals tend to live. But what are the possible implications for humans? See my video Methionine Restriction as a Life Extension Strategy.
I’ve talked before about the free radical theory of aging, the concept that aging can be thought of as the oxidation of our bodies just like rust is the oxidation of metal (see Mitochondrial Theory of Aging). Methionine is thought to have a pro-oxidant effect. The thinking is that lowering methionine intake leads to less free radical production, thereby slowing aging. Fewer free radicals would decrease the rate of DNA damage, which would curtail the rate of DNA mutation, slowing the rate of aging and disease and potentially increasing our lifespan.
There are three ways to lower methionine intake: The first is caloric restriction. By decreasing our overall intake of food, we would reduce our intake of methionine. Or, because methionine is found protein, we could practice protein restriction, eating a relatively protein deficient diet. The third option is eat enough food, eat enough protein, but just stick to proteins that are relatively low in methionine, which tends to mean plant proteins.
Caloric restriction is hard, because we walk around starving all the time. Something like every-other-day eating is described as “never likely to gain much popularity as a pro-longevity strategy for humans, so it may be more feasible to achieve moderate methionine restriction by eating a plant-based diet.” On a population-wide level, folks could benefit from just lowering their protein intake, period. Researchers noted that “the mean intake of proteins [and thus methionine] of Western human populations is much higher than needed. Therefore, decreasing such levels has a great potential to lower tissue oxidative stress and to increase healthy life span in humans while avoiding the possible undesirable effects of caloric restriction.”
We’re eating around double the protein we need, so the first thing doctors can recommend is to decrease the intake of protein, but we can also get our methionine even lower by eating a plant-based diet.
The fact that beans have comparably low methionine has been classically considered a disadvantage. But, given the capacity of methionine restriction to decrease the rate of free radical generation in internal organs, to lower markers of chronic disease, and to increase maximum longevity, this “disadvantage” may actually be a strong advantage. This fits well with the important role of beans in healthy diets like the traditional Mediterranean diet. Interestingly, soy protein is also especially poor in methionine, which may help explain the healthy effects iof soyfoods. Watch my video Increased Lifespan from Beans.
The reason why plant-based diets are so protective is not known. Yes, vegetables contain thousands of phytochemicals, but separately investigating their possible protective roles would be an impossible task. The idea that the protective effect is not due to any of the individual plant food components, but to a synergic “combined effect” is gaining acceptance. However, based on the relationship of excess dietary methionine to vital organ toxicity, as well as its likely mechanism of action through increases in free radical generation, the possibility exists that the protective effects of plant-based diets can be due, at least in part, to their lower methionine content. As one paper concluded, “The low-methionine content of vegan diets may make methionine restriction feasible as a life extension strategy.”
Plant-based diets can also mimic other benefits of caloric restriction, such as improving levels of the “fountain of youth” hormone DHEA. See The Benefits of Caloric Restriction Without the Actual Restricting.
Americans are living longer but sicker lives. That’s why we need a diet and lifestyle that supports health and longevity. I have a whole presentation on the role diet can play in preventing, arresting, and even reversing many of our top 15 killers: Uprooting the Leading Causes of Death.
I’ve touched previously on the irony that animal protein may be detrimental for the same reasons it’s touted as superior in Higher Quality May Mean Higher Risk.
-Michael Greger, M.D.
PS: If you haven’t yet, you can subscribe to my free videos here and watch my 2013 live year-in-review presentation More Than an Apple a Day.
A Low Methionine Diet May Help Starve Cancer Cells
When designing an antibiotic, we can’t create a drug that destroys DNA because that’s something that both humans and bacteria share in common. It would kill bacteria, but it might kill us, too. Instead, many antibiotics work by attacking bacterial cell walls, which is something bacteria have that we don’t.
Similarly, antifungals can attack the unique cell walls of fungus. Pesticides can work by attacking the special exoskeleton of insects. But fighting cancer is harder because cancer cells are our own cells. So fighting cancer comes down to trying to find and exploit differences between cancer cells and normal cells.
Forty years ago, a landmark paper was published showing for the first time that many human cancers have what’s called “absolute methionine dependency,” meaning that if we try to grow cells in a Petri dish without giving them the amino acid methionine, normal cells thrive, but without methionine, cancer cells die. Normal breast cells grow no matter what, with or without methionine, but cancer cells need that added methionine to grow.
What does cancer do with the methionine? Tumors use it to generate gaseous sulfur-containing compounds that, interestingly, can be detected by specially trained diagnostic dogs. There are mole-sniffing dogs that can pick out skin cancer. There are breath-sniffing dogs that can pick out people with lung cancer. Pee-sniffing dogs that can diagnose bladder cancer and–you guessed it–fart-sniffing dogs for colorectal cancer. Doctors can now bring their lab to the lab!
It gives a whole new meaning to the term “pet scan.” :)
Methionine dependency is not just present in cancer cell lines in a Petri dish. Fresh tumors taken from patients show that many cancers appear to have a biochemical defect that makes them dependent on methionine, including some tumors of the colon, breast, ovary, prostate, and skin. Pharmaceutical companies are fighting to be the first to come out with a drug that decreases methionine levels. But since methionine is sourced mainly from food, a better strategy may be to lower methionine levels by lowering methionine intake, eliminating high methionine foods to control cancer growth as well as improve our lifespan (see Methionine Restriction as a Life-Extension Strategy).
Here’s the thinking: smoking cessation, consumption of diets rich in plants, and other lifestyle measures can prevent the majority of cancers. Unfortunately, people don’t do them, and as a result hundreds of thousands of Americans develop metastatic cancer each year. Chemotherapy cures only a few types of metastatic cancer. Unfortunately, the vast majority of common metastatic cancers, such as breast, prostate, colon, and lung, are lethal. We therefore desperately need novel treatment strategies for metastatic cancer, and dietary methionine restriction may be one such strategy.
So, where is methionine found? In my video, Starving Cancer with Methionine Restriction, you can see a graph of foods with their respective methionine levels. Chicken and fish have the highest levels. Milk, red meat, and eggs have less, but if we really want to stick with lower methionine foods, fruits, nuts, veggies, grains, and beans are the best. In other words, “In humans, methionine restriction may be achieved using a predominately vegan diet.”
There are also compounds in animal products that may actually stimulate tumor growth. See, for example, How Tumors Use Meat to Grow: Xeno-Autoantibodies. Animal protein may also boost levels of the cancer-promoting hormone IGF-1 (The Answer to the Pritikin Puzzle). Combined, this could all help explain why plants and plant-based diets have been found effective in potentially reversing some cancer processes. See Cancer Reversal Through Diet?, Strawberries versus Esophageal Cancer, and Black Raspberries versus Oral Cancer.
So why isn’t every oncologist prescribing a low-methionine diet? One researcher notes that “Despite many promising preclinical and clinical studies in recent years, dietary methionine restriction and other dietary approaches to cancer treatment have not yet gained wide clinical application. Most clinicians and investigators are probably unfamiliar with nutritional approaches to cancer.” That’s an understatement! “Many others may consider amino acid restriction as an ‘old idea,’ since it has been examined for several decades. However, many good ideas remain latent for decades if not centuries before they prove valuable in the clinic….With the proper development, dietary methionine restriction, either alone or in combination with other treatments, may prove to have a major impact on patients with cancer.”
Why might the medical profession be so resistant to therapies proven to be effective? The Tomato Effect may be partially to blame.
In my video, Anti-Angiogenesis: Cutting Off Tumor Supply Lines, researchers come to the same plant-based conclusion from a different perspective, starving cancers of their blood supply.
-Michael Greger, M.D.
PS: If you haven’t yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death and More Than an Apple a Day.
Image Credit: PNNL – Pacific Northwest National Laboratory / Flickr
