Chapter 24
Cold Turkey
Let’s say you want to build a really big cube, and someone dumps a pile of little cubes in front of you. Fine. You stack them, and you’re done in no time. But what if instead you get a pile of pyramids? Sure, the pyramids can be taken apart. You would still have the essential elements for your big cube, but you probably still wouldn’t throw yourself at the pyramids with the same enthusiasm because it’s a lot more work to break them down first. Basically, the same thing happens with your liver and IGF-1.
All plant proteins and almost all animal proteins are complete proteins that contain all nine essential amino acids. (The only incomplete protein in the food supply is animal protein collagen [gelatin], which lacks tryptophan.) So you couldn’t live on Jell-O and marshmallows, but all other proteins in food, whether from plants or animals, contain all the necessary building blocks. When you hear about high or low protein quality, that refers to the relative proportions of the different essential amino acids. The more these proportions match our own proteins, the higher the quality is rated.
In a certain sense, there is only one truly “perfect protein” for humans: human flesh. Otherwise, any other meat will do. We are not cannibals, but by helping ourselves in the animal kingdom, or when we eat other mammals, we are ingesting protein that is more similar to our own than, for example, that of a kidney bean. That is not necessarily a good thing.
When a big load of incoming proteins hits the liver, it proceeds analogous to the head start we have with the cubes from the building set: The protein is meat, and we are also meat, so we start pumping out IGF-1 to speed up cell division so that the excess gets used up. But if we get plant proteins, they are like the pyramids. Our body can split them into all the essential amino acids we need, but they simply don’t set off the same building boom as animal protein. This phenomenon does not seem to have any influence on muscle mass, because people who suffer from acromegaly (a form of IGF-1-induced giant growth of certain body parts) are not excessively muscular, and people who are injected with IGF-1 twice daily for a year do not experience an increase in lean mass or muscle strength. But the steep rise in IGF-1 in connection with the consumption of animal protein can very well affect life expectancy and cancer risk.
What about soy protein?
How about the few plant proteins whose amino acid profile resembles animal protein, for example soy? One of the selling points for soy is its “high protein quality,” but with IGF-1 the supposedly higher quality could also mean higher risk. Does this apply to soy-based protein?
We know that consumption of animal protein is associated with considerably higher amounts of IGF-1, while eating plant protein not derived from soy is associated with significantly lower levels. Soy protein lies in the middle and shows no significant association with IGF-1 levels. So if we replace animal protein with soy protein, we may not experience as dramatic a drop in IGF-1 as we achieve with substitution by other plant proteins. This was confirmed by a Stanford study: A switch from regular beef, pork, and chicken to plant-based (Beyond Meat) beef, pork, and chicken analogs made from soy and pea protein brought about only an insignificant decline in IGF-1 (by 3 percent).
Intervention studies in which large amounts of soy protein (40 g daily) were supplemented caused IGF-1 levels to rise, but eating a few servings of real soy-based foods did not. The upper limit seems to be around 25 grams of soy protein daily. Of course, the main reasons we worry about IGF-1 are cancer and life expectancy, and soy eaters seem to be protected against cancer. A recent review with meta-analysis found that an association exists between a daily intake increased by 5 grams of soy protein, for example three quarters of a cup of soy milk or two tablespoons of baked “soy nuts” (dry-roasted soybeans), and a 12 percent lower number of deaths from breast cancer. Soy foods also seem to protect against prostate cancer. As for longevity: In Part II we will explore in more detail that two of the longest-lived officially studied population groups worldwide—namely the Japanese on Okinawa and the vegetarian Seventh-day Adventists in California—eat soy foods daily.
Cold Turkey
IGF-1 explains in part why the lives of some people are shorter when they follow certain low-carb diets, but those of others are not. In a Harvard cohort study of twins, it was found that with low-carb diets high in vegetables, the mortality rate was lower, whereas with animal sources the risk of premature death grew by 23 percent and specifically the risk of dying of cancer grew by 28 percent. Just replacing 5 percent of calories from animal protein with plant protein, for example in beans or nuts, could reduce the risk of early death by 14 percent (and the risk of dying of dementia by 19 percent). The worst is protein from eggs (especially egg white). Men would have a 24 percent lower risk of dying early, and women 21 percent, if they replaced 3 percent of egg protein with plant protein.
When a dream team of aging researchers, including Luigi Fontana and Valter Longo, followed a nationally representative sample of thousands of Americans over 50 for an average of 18 years, they found that participants under 65 with a high protein intake had a 75 percent increased overall mortality and a fourfold increased risk of dying of cancer. However, when they looked at the plant protein sources and the animal ones separately, it turned out that the overall risk of death was limited to consumption of the animal proteins. The sponsoring university summed up the study in a memorable opening sentence: “The chicken wing you eat could be as deadly as a cigarette.”
The researchers explained that on a diet high in animal proteins, someone in middle age had a fourfold greater risk of dying of cancer than someone who ate only little protein. That was comparable to smoking. And by “little protein” they are referring to what most people eat. The “little protein” group actually consumed the recommended amount, namely 0.8 grams per kilo of healthy body weight, or 50 grams daily for someone who weighs about 140 British pounds (63.5 kilos)—preferably from plant sources to keep IGF-1 activity low. All in all, it is estimated that every hamburger we eat costs us as much lifespan as two cigarettes.
Two risks do not cancel each other out
How did scientists react to the revelation that the Guardian phrased in a headline like this: “Meat, eggs and dairy could be as harmful to health as smoking”? A nutrition scientist explained that it was “dangerous” to compare the effects of smoking with those of animal foods because a smoker might think: “Why should I quit smoking if my ham-and-cheese sandwich is just as bad for me?”
That reminds me of a famous Philip Morris cigarette ad that tried to play down the dangers of smoking. It argued that some believe secondhand smoke is harmful (it increases lung cancer risk by 19 percent), but drinking a glass or two of milk every day is much more harmful (a 62 percent higher lung cancer risk). So it concluded: “Let’s keep things in perspective.” The ad went on to explain that the cancer danger from secondhand smoke might be “significantly below the risk that … is assumed for many everyday objects and activities.”
That’s like claiming it’s not so bad to be stabbed, because being shot is much worse. (Note: Philip Morris stopped vilifying dairy products after it bought Kraft Foods.)