July 2016 update: A new study in mice and 19 men by longevity researcher Luigi Fontana found that restricting daily protein to 7 to 9 percent of calories improved their metabolic health.  

Legumes–beans, peas and lentils — are the #1 key to longevity, says Dan Buettner, the bestselling author who’s been studying the world’s Blue Zones, those pockets of the world  (Mediterranean, Japan, California, Costa Rica) where people eating plant-based diets with legumes as their main source of protein are outliving us all. 

How might legumes fuel longevity? Could some be more “nutritarian” than others? How much protein should you be eating anyway? And must it be all plants all the time?

Legumes for Protein:  Phytos, Fiber  & More  Glycine, less Meth

Unlike their animal counterparts, plant sources of protein contain phytonutrients and phytic acid and fermentable fiber, which all help regulate inflammation, the lowest common denominator of modern disease. 

Amino acids are also important. In the first post of this series, we panned excess methionine, the sole amino acid to produce free radicals of oxygen—and praised glycine, which inhibits inflammation and may be methionine’s antidote.  Other amino acids, including leucine and glutamine, also fuel the inflammatory cell signalling process that causes cancer cells to grow and spread. 

Compare a serving of legumes (1/2 cup cooked) to a serving of animal foods (3  oz–a  deck of cards.)  Legumes contain a fraction of the methionine, leucine and glutamine –and their glycine is high while their meth is low–a 3:1 ratio.  In animals, glycine concentrates in bone and connective tissue, parts we don’t usually eat.  

Some legumes do even better than 3:1 in their glycine: meth ratios:

• fava beans: 5:1
• lentils: almost 5:1 (Choose the red ones. They’re higher in phytonutrients.) 
• split peas: 4+:1
• tempeh: 4+:1

Both tempeh and natto—fermented soybeans– have another life-extending quality. They’re great sources of spermidine, also known as the “longevity elixir.”  It’s no coincidence that word conjures up images of those tiny, powerful swimmers. 

So named because it was first identified in sperm, spermidine causes your cells to undergo autophagy, a process of cellular housekeeping that removes bad cells and inhibits inflammatory cell signalling. Several studies have shown that autophagy is important for controlling cancer growth.

All legumes in fact are rich in spermidine; the process of fermentation increases it. On the other hand, saturated fat, which concentrates in animals and tropical oils, depletes your body of spermidine.

How much protein?  

So how much protein should you consume each day? What factors does that depend on? 

Too much protein!

Adults in the US and Northern Europe are consuming almost twice as much protein as they really need, according to longevity researchers Drs. Valter Longo and Luigi Fontana.  Many people get 15% or more of their calories from protein—and for most people, that’s way too much, they say. Ten percent of calories from protein–the current minimum suggested by the US government for adults 19 to 70–should be the maximum, they propose.

That works out to around .7- .8 grams for every gram (about 2.2 lbs) of body weight–or about 46 to 56 grams of protein a day.

Age matters: Maintain muscle! 

If you’re over 65 or 70, however, depending on your health status, you probably need to increase that amount. “(A)t older ages, it may be important to avoid low protein intake and gradually adopt a moderate to high protein possibly mostly plant based consumption to allow the maintenance of a healthy weight and protection from frailty,” Longo and other researchers say.

In a recent study examining the diets of adults over age 50, scientists found that high protein diets (more than 20% of calories from protein) were associated with 75% greater mortality and 4 times the cancer incidence of low protein diets (less than 10% of calories from protein), with one important exception: In people over 65, a protein intake of 10 to 20 percent of calories meant longer life. 

The difference in age categories may be due to how well we maintain muscle.  As we get older, our bodies are less efficient at using protein–and that’s often because our muscles start to atrophy. By doing resistance training, you can help build muscle and keep your body burning fuel more efficiently. By spreading protein intake throughout the day rather than loading up on it in one meal, your body will also do a better job of building muscle and thus burning fuel.  

What if you have cancer?

If you have cancer, how much total protein should you be eating? Scientists are just starting to study that question, and the answer appears to be: Keep it low.   

Drs. Longo and Fontana have done studies on animal models with breast and prostate cancer. Compared to diets containing 20% protein from animal sources, diets with 20% plant protein inhibited tumor weight about 37% percent. But diets containing even less protein (7 %, the minimum the animals could tolerate and still maintain health and weight) inhibited tumor growth even more significantly– over 50% for breast cancer, 70% for prostate cancer, a result they called “striking.”  

“Our findings suggest that a reduction in dietary protein intake is highly effective in inhibiting tumor growth (in the animal models),” they said, even when the diet was started after the tumors were established.  The inhibition in prostate cancer growth induced by protein restriction “appears to be greater than the effect induced by fat or carbohydrate restriction previously reported by other groups and similar to the inhibitory effect induced by calorie restriction,” they wrote.  

Australian researcher Dr. Paul Cavuoto provides another clue.  “ If I had cancer, I would certainly seek to restrict methionine in my diet, probably to 1 gram a day (so long as I don’t become deficient in key vitamins and nutrients),”  he told me.

If you have cancer, talk with your doctor about the recent research suggesting low protein and low methionine may be important. Drugs to inhibit the cell signalling that proteins stimulate are also available.  If you’re in treatment (chemo or radiation) or are losing muscle, you may need more protein than other survivors. Resistance training and spreading protein throughout the day are strategies that can help. And if you do opt for more than 10% of your calories from protein, the Longo-Fontana study suggests that plant proteins are best.  

 Must everybody consume all plants all the time?

If you insist on a high protein diet (more than 10% of calories from protein), the study that looked at the diets of people over 50 suggests that plant proteins are best. But the Longo-Fontana study on animal models found an answer that may surprise you: If you keep dietary protein low (below 10% of calories), animal protein may be fine.  

“Interestingly, there was no additive effect of switching from animal to plant proteins when dietary protein content was 10%, suggesting that a threshold exists below which the amino acid composition is less important than the protein content of the diet,” the authors said.

I’d add one caveat: Restrict methionine to hedge your bets. It turns you into a coal-burning furnace. It’s the one amino acid that damages your cells’ mitochondria, the part that controls how cells burn fuel for energy, and that causes you to produce free radicals of oxygen, molecules that damage cells. Free radicals both cause cancer and cause cancer to grow.   

To restrict methionine, you’ll need to minimize or eliminate animals. And if you have cancer, you may also want to limit plant foods rich in methionine, including:

• Brazil nuts (Yes, I know they’re touted for selenium, but you can get selenium from alliums and crucifers.)  
• flour made from sesame or sunflower seeds–or large amounts of their seeds or butters 
• soy protein concentrate and isolate (used to make other foods. Check labels.)

To calculate food contents yourself, use the nutrient search tool at nutritiondata.com or sign up for the free program at cronometer.com.   

 Legumes: The Bottom Line

So let’s say you’re eager to make legumes your main source of protein–and you’re aiming to keep protein low (below 10 percent of calories, around 46  grams a day for women, 56 for men.) How much legume should you consume each day? 

The Blue Zoners may provide an answer. They eat on average a cup of cooked legumes daily. But Blue Zoners are not purists. They also eat small amounts of animal protein—a three ounce serving, the deck of cards, around once a week. 

If you’re keeping protein to a minimum and opt for a little animal food occasionally, make sure it counts. Choose animals rich in zinc and/or long chain omega 3 fatty acids, two healthy components that are hard to get when you eat only plants.

It’s your patterns that are most important in reducing cancer risk, says Dr. Steven Zeisel, director of the University of North Carolina’s Nutrition Research Institute and an advocate of plant-based patterns. 

Next on the anti-cancer platter: Flavonoids Fight Cancer  These powerful phytonutrients are yet another reason why certain plants should pop on your anti-cancer plate.    

© 2016 Harriet Sugar Miller