Researchers at the Penn State College of Medicine believe that the health and longevity benefits seen in animals on sulfur amino acid-restricted diets could also work in humans. The concept of dietary sulfur amino acid restriction has been of interest to researchers for almost 30 years when the first studies showed health benefits in animals placed on methionine-restricted diets.
Amino acids are the building blocks of all proteins in our body, and methionine and cysteine both belong to a subgroup known as the sulfur amino acids. These help the body to create various proteins and are involved in metabolism.
Having your cake and eating it
It has long been known that animals on a calorically restricted diet tend to live longer and are healthier. Caloric restriction means eating around 20-25 percent less but without incurring malnutrition or a reduction in essential nutrients. The problem is translating those benefits to humans, as it is very difficult to get people to stick to a calorically restricted diet; this is why researchers have been seeking ways to mimic the effects of such a diet without getting people to eat less.
A recent comprehensive review of sulfur amino acid restriction publications shows that this approach has a range of benefits, including increased lifespan, without the need to use caloric restriction .
The data shows that methionine restriction is linked to a slower rate of aging and increased lifespan in yeast, fruit flies, rodents, and human cells. Sulfur amino acid-restricted diets have shown health benefits in animals, such as reduced levels of fat and oxidative stress, reduced cancer incidence, and improved insulin sensitivity.
Sulfur amino acids are important for growth, so restricting the amount available in the diet slows down that growth; this leads to smaller animals that typically live healthier and longer. This stunted growth is a concern for translation to humans and has, until now, been a bottleneck to progress.
Fortunately, a lot of the health benefits are seen when a sulfur amino acid-restricted diet is started in adult animals that have developed normally, bypassing the stunted growth issue. Additionally, these studies observed no other serious side effects of this diet. This strongly suggests that we might be able to translate this approach to humans, which is why the Penn State researchers are currently conducting a human trial of dietary sulfur amino acid restriction.
It is worth mentioning at this point that sulfur amino acids are found in protein-containing foods, so avoiding them is not an easy task. However, vegan diets are low in methionine and cysteine, as they include beans and other legumes that contain protein but are low in sulfur amino acids.
It is unlikely that restricting sulfur amino acids will enhance lifespan in humans as much as we see in animals. This is similar to exercise and caloric restriction, which are reliable ways to moderately slow the aging process down to stay healthier for longer.
However, given that more robust technologies are still some years or even decades out in some cases, this presents some low-hanging fruit. If we can use such approaches to add a few additional years, that could make all the difference in being alive upon the arrival of true rejuvenation biotechnologies, which directly repair the damage that aging does to the body.
 Dong, Z., Sinha, R., & Richie, J. P. (2018). Disease prevention and delayed aging by dietary sulfur amino acid restriction: translational implications. Annals of the New York Academy of Sciences.