The link between MTHFR and homocysteine is clear – if you aren’t familiar with that part of the picture, you can brush up with last week’s topic. The link between methionine and homocysteine is clear as well since they loop together in the methionine cycle with dietary methionine converting into homocysteine as a by-product, then being recycled back to methionine using MTHFR.
It’s easy to get into a situation where you assume methionine is “good” and homocysteine is “bad,” but actually for MTHFR, methionine itself is a double-edged sword.
Recommended Intake of Methionine
When it comes to suggested protein intakes per day, it’s pretty hotly debated and the criteria are updated every few years. Generally, requirements for infants are much higher (according to intake in mg/kg body weight) than those of children, and children are in turn higher than those of adults. Again, this is based on an mg/kg measure and not an absolute number.
- Infants (3-4 months) – 58 mg/kg body weight/day
- Children 2 years old – 27 mg/kg body weight/day
- Children 10-12 years old – 22 mg/kg body weight/day
- Adults – 13 mg/kg body weight/day.
This means for the average 150 pound (or 68 kg) adult, the daily requirement for methionine is 884 mg. That is found in 100 g (or 3.5 oz) or less of a lot of meats. This means that while vegetarians are probably getting the right amount, most meat eaters are significantly overdoing it.
Recommended Daily Protein Intake
This data is also debated, but the best researched reference data from the World Health Organization is below.
|Age||Protein intake in grams/kg body weight/day|
|Infant||1.2-1.4 g/kg body weight/day|
|Children||0.8 – 0.97 g/kg body weight/day|
|Adolescents||0.67 – 0.79 g/kg body weight/day|
|Young Adult||0.75 g/kg body weight/day|
|Adult||0.6 g/kg body weight/day|
|Elderly||0.75 g/kg body weight/day|
|Pregnant||0.92 g/kg body weight/day|
|Lactating||Basic rate plus 15 g per day for the first 6 months, 12 g per day thereafter.|
This works out to about 46 grams per day for the average woman and 56 grams per day for the average man. In the west, we tend to overdo protein. Most American adults eat about 100 g of protein per day, which is twice the recommended amount. Not only that, the latest trends in nutrition mean that 60% of Americans report that they are trying to increase their protein intake according to the Hartman Group.
Food Sources of Methionine
Methionine is an amino acid, which is the building block of protein, so naturally, it is high in protein-rich foods. The top ten categories of foods according to my food data are:
|Methionine per 6 oz||Similar Foods|
|Ground Turkey||931 mg||1583 mg||Chicken breast, thigh, drumstick.|
|Beef (skirt steak)||905 mg||1539 mg||Other cuts of beef, lamb, veal, buffalo|
|Tuna||885 mg||1505 mg||Grouper, salmon, snapper, tilapia, mahi mahi|
|Lean Pork Chops||850 mg||1445 mg||Pork ribs, lean ham, pork bratwurst,|
|Firm Tofu||211 mg||532 mg||Edamame, soybean sprouts, soy milk|
|Milk||88 mg||431 mg||Yogurt, buttermilk|
|Low fat ricotta||284 mg||528 mg||Parmesan, gruyere, Swiss (other cheeses)|
|Brazil nuts||1124 mg||1914 mg||Hemp, squash, pumpkin, chia, sesame seeds.|
|Large white beans||146 mg||196 mg||Navy, kidney, black beans.|
|Quinoa||96 mg||133.5 mg||Teff, wild rice, kamut.|
So… Too Much Protein?
In the West, we love our protein. We’re all working on building muscle and improving our lean bodyweight… Except that in reality, most of us aren’t. Most of us are actually working on holding down our office chair and staring at a screen. Still, we’re obsessed with the idea of being fit and lean so we overconsume in different ways than we used to. Most of us eat more than we need in general, and those of us who are “working on our health” are especially prone to working to get too much protein This, of course, leads to the modern issues of obesity and heart disease,
For people with an MTHFR issue, this takes on an added dimension because eating more protein means adding more burden to the methionine (or methylation) cycle and hence the MTHFR enzyme which ties methylation into the folate cycle. Remember how those two cog together like gears?
Extra protein means your folate cycle has to work harder, your body needs more active folate and more methyl donors, and homocysteine is going to build up. We already talked about how bad homocysteine is when it builds up.
Plus, Lower Methionine Intake Might Mean You Live Longer
Research has long shown that calorie-restricted diets are effective in promoting lifespan. Meaning, the people who eat less usually live the longest, even to the fact that some of the humans with the longest life spans on record have gone through periods of food shortage. Further research has found that limiting methionine intake specifically extends lifespan. That is with or without actual calorie restriction. Also, intermittent fasting, which is one of my favorite health hacks, is a great way to actually have minor calorie restrictions without too much fuss.
Also, methionine restriction is showing promise as a therapeutic approach to limiting the growth of certain types of cancer. This isn’t because methionine is bad – it’s essential for human growth, development, and healthy functioning. We do get more than we need, but also cancer cells have fewer ways to adapt to methionine limitation, while healthy cells can protect themselves better.
In a fascinating study, researchers are also limiting methionine with the use of an oral medication that breaks down methionine (called an oral methionase) to treat Covid-19. The RNA of the coronavirus needs to be methylated, using SAMe, in order to initiate viral replication. Limiting methionine (which limits SAMe) interferes with that step and so slows the viral replication and can potentially reduce viral load. This generally makes me wonder about all of us MTHFR folks and Covid-19. Do we have a survival advantage because it’s harder for us to produce SAMe? Also, should people supplementing with SAMe consider taking a break if they’re in a high-risk situation for COVID?
Even though we are obsessed with getting more protein – I mean, who doesn’t have jerky in their purse right now? We are clearly overdoing it. Reducing protein intake, specifically methionine, would help us all live longer, healthier lives. But it is especially important for MTHFR folks.