"He who does not know food, how can he understand the diseases of man?" ~Hippocrates
Caloric restriction has been a hot topic in my course on “Aging” this past week, as it is a scientifically-proven method for prolonging life.
I also learned about another method for increasing longevity, and it has to do with the amino acid methionine. Here is a summary of the presentation I gave on it today:
**Note: I apologize for the technical nature of this post... if not interested in minutiae, please jump to the end for the short summary!**
Food with a high methionine content
Food with a low methionine content
What is methionine?
- An essential amino acid
- One of two sulfur containing amino acids
- In the metabolic pathway of S-adenosyl methionine (SAM) and homocysteine
- An intermediate in the biosynthesis of cysteine, carnitine, taurine, lecithin, phosphatidylcholine, and other phospohlipids
- Most fruits, vegetables, and legumes contain very little methionine
- Meats, fish, eggs, and some plant seeds have high levels of methionine
This study from 1993 showed that cutting dietary methionine by 80% in rats increased longevity by greater than 40% in both mean and maximal lifespan. The rats had free access to food and ended up eating more calories per gram of body weight. They were not calorie-restricted.
More recently, other researchers have confirmed these results and found that methionine-restricted mice (with normal calorie intake) had:
- Lower levels of IGF-1, insulin, glucose, and thyroid hormones (these changes are also found in calorically restricted animals)
- Delayed onset of clouding of the lens in the eye (cataracts)
- Delayed immune system changes (changes in T cell subsets)
- Livers more resistant to oxidative stress
- Decreased levels of mitochondrial oxidative damage
The following mechanisms have been suggested to explain these longevity findings from low-methionine diets:
- Endocrine changes including decreased IGF-1, T4, glucose, and insulin (all of which are important in the aging process)
- Hormesis (chronic low levels of stress builds “immunity” against bigger stressors)
- Changes in levels of s-adenosyl methionine (SAM) and homocysteine (thought to play a role in neoplastic, cardiovascular, and other aging-related diseases)
- Changes in glutathione (glutathione is protective against oxidative damage)
- General decline in protein synthesis (may be protective against age-related decline)
What might this mean for humans?
The vegan diet (which includes no animal products) is low in methionine. Here is why:
- The methionine content of plant proteins, legumes, soy, and nuts is lower than in animal proteins
- The overall protein content of plant-derived foods is lower than animal-derived foods
- Plant proteins are digested less efficiently than animal proteins
- Vegans have lower IGF-1 levels (suggested to be a “pacesetter” in the aging process”)
- Vegans have lower insulin levels (lower insulin levels leads to lower levels of IGF-1)
- Vegans have lower rates of diseases of aging, including cancer, diabetes, and cardiovascular disease
- A low-methionine diet in animal models has been proven to delay the aging process
- Vegan diets are low in methionine, and human studies on vegans provide some evidence for increased longevity in this population
- There are many remaining questions, and some of mine include: Calorie-restriction versus methionine-restriction – are they additive? What is the impact of methionine-restriction on fertility? How does methionine-restriction impact telomere length/telomerase activity?
I am curious about what the Calorie Restriction Society would think about this. Are there any Methionine-Restriction Societies? This idea of methionine-restriction might be something The Vegan Society could discuss/advertise.