By Rui Wang
January 22, 2021 -- High-protein diets
are having a moment. In any grocery store you can now buy a protein bowl, pick
up a protein box of eggs and nuts for lunch, or snack on a protein bar.
But there’s evidence that restricting
which proteins you eat — particularly cutting back on meat — could be important
for healthy aging. The surprising reason: it forces the tissues to make
hydrogen sulphide (H2S), a gas that’s poisonous if inhaled and smells like
rotten eggs, but promotes health inside the body.
As a physiology researcher, I have long
been interested in the strange role of H2S in the body. This is not a gas
anyone wants around. It stinks, is a component of flatulence, and its toxicity
has been linked to at least one mass extinction.
And yet, the body naturally produces
small amounts of it as a signalling molecule to act as a chemical messenger.
Now, we are starting to understand the link between diet and H2S production.
Diet restrictions that increase
longevity
Less can be more when it comes to food.
When scientists have put organisms on carefully balanced but restricted diets,
these organisms have substantially increased healthy lifespans.
This holds true for yeasts, fruit flies,
worms and monkeys. In mice, such diets reduce cancer risk, strengthen the
immune system and improve cognitive function.
But because aging and longevity are
complex processes, it has been difficult for researchers to pin down the
mechanisms at work. Recent studies have shed new light, and it is apparent that
H2S plays a crucial role.
Studies since the 1990s have shown that
reducing intake of certain sulphur-containing amino acids, the building blocks
of proteins, can increase longevity in rats by around 30 per cent. More
recently, a collaborative team involving me and led by scientists at Harvard,
performed a series of animal studies in which we restricted the intake of two
sulphur amino acids — cysteine and methionine — to study what effects this had.
It caused the animals to ramp up
production of H2S in their tissues, which triggered a cascade of beneficial
effects. These included increased new blood vessel generation, which promotes
cardiovascular health, and better resistance to oxidative stress in the liver,
which is linked to liver disease.
But it remained to be seen whether
similar effects would occur in humans. Earlier this year, a study using data
from the 11,576 adults in NHANES III, the U.S. national nutrition survey, delivered
evidence that they do. It found that reduced dietary intake of these sulphur
amino acids is linked to lower cardiometabolic risk factors, including lower
levels of cholesterol and glucose in the blood. Cardiometabolic risk factors
are those linked to heart disease, stroke and diabetes.
The upshot of this research is that
there’s good evidence that limiting intake of foods containing high levels of
sulphur amino acids can reduce the risk of chronic diseases like diabetes and
heart disease, and promote healthy aging. In North America, most of us are a
long way from achieving this. Because these sulphur amino acids are abundant in
meat, dairy and eggs, which feature prominently in our shopping carts, we eat
on average 2.5 times our daily requirement of them.
Red meat is particularly high in sulphur
amino acids, but fish and poultry white meat also contain a lot (the dark meat
has less). Switching to plant-based proteins would help reduce this intake.
Beans, lentils and legumes are good
sources of protein that are also low in sulphur amino acids. But beware: soy
protein, which is the basis of foods like tofu, is surprisingly high in sulphur
amino acids. Meanwhile, vegetables like broccoli contain lots of sulphur but
not in amino acid fo
One important caveat is that sulphur
amino acids play vital roles in growth, so children should not adopt diets that
are low in them.
Other roles for H2S
It might seem odd that a toxic gas can
help maintain health, but it may reflect the origins of life on early Earth
when the atmosphere was much richer in sulphur gas than it is today. Indeed, we
are starting to appreciate how fundamental H2S signalling may be. For example,
it has also been shown to reduce inflammation, opening the door to potential new
treatments for arthritis or potential use as a painkiller.
The trick is delivering H2S where it’s
needed — safely. Several pharmaceutical companies are working on compounds that
bind it while in transit through the body, and release it in tiny doses in the
tissues. In time, these could be used as preventive measures to support healthy
aging. This would be useful because the drawback of a low-sulphur amino acid
diet is that humans are notoriously bad at sticking to such plans long-term.
In the lab, we can control experimental
diets. In the real world, people snack or grab a burger when they don’t want to
cook. If delivery mechanisms can be made reliably and cheaply enough, it could
be possible to gain the health effects of increased tissue H2S without
dictating what people eat.
Rui
Wang, Dean, Faculty of Science, York
University, Canada
This article is republished from The
Conversation under a Creative Commons
license. Read the original
article.
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