Key takeaways:
- The CBS gene impacts the transsulfuration pathway and influences homocysteine levels.
- Despite a lot of popular advice promoting a low-sulfur diet for CBS variants, there isn’t much research that backs this up.
- Studies show that CBS gene variants may have minimal effects on cholesterol and cleft lip risks.
- One specific mutation in CBS is linked to high homocysteine levels, and vitamin B6 has been shown to help people with this variant. You can check your raw data for this in the genotype report.
CBS Gene: Does Research Show that You Should Eat a Low Sulfur Diet?
What is the CBS gene?
The CBS gene – cystathionine beta-synthase – codes for the CBS enzyme that acts within the transsulfuration pathway. The CBS enzyme reduces homocysteine to an intermediate (cysteine) that eventually can become glutathione, an important antioxidant in the body. Additionally, the CBS enzyme participates in a desulfation reaction to help create hydrogen sulfide, H2S. Hydrogen sulfide, a molecule needed by the body in just the right amount, at low levels, acts as a mitochondrial electron donor, but at high levels, it is poisonous to the mitochondria. Likewise, the importance of the body maintaining the right levels of homocysteine should not be understated because high levels of homocysteine are associated with heart disease.[ref]
Changes in CBS enzyme production show connections to various problems, including cardiovascular disease and immune system problems. Decreased CBS causes homocysteine levels to rise, leading to homocystinuria.
Something to note here: Vitamin B6 is a cofactor needed in the reaction that converts homocysteine.
What do online clinicians say about the CBS gene?
CBS is often mentioned on websites that discuss the methylation cycle, with speculation by a couple of well-known clinicians that some of the variants listed below upregulate or increase the amount of the CBS enzyme. Websites that discuss these clinicians’ ideas often caution that people with CBS upregulation variants should avoid eating foods that contain sulfur (meat, garlic, eggs, etc.) and warn of too much ammonia.[ref][ref]
Note that I found no research studies that show that the common CBS variants indicate that sulfur foods should be restricted.
What does the research actually show on the CBS variants?
The research on the variants:
- does not show that these variants are a problem
- does not indicate that everyone with the variants should be on low-sulfur or low-protein diets
- does not show that people with the variants should shell out money for specific ammonia-reducing supplements
Instead, the research indicates that the common CBS variants may have a subtle effect on cholesterol levels. One of the variants slightly decreases the risk of having a baby with a cleft lip, which indicates a positive connection to the methylation cycle.[ref][ref]
CBS Genotype Report:
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Lifehacks:
The most impactful variant above is the rs5742905 variant, which increases the risk of high homocysteine.
When to test your homocysteine levels:
There is a well-researched connection between high homocysteine levels and an increased risk of heart disease as well as other health impacts. If you do have the variant and high homocysteine levels, the good news is that vitamin B6 is likely to help.
Related article: Homocysteine: research studies and genetic connections
If your data shows the rare rs5742905 G allele, you may want to get your homocysteine levels checked. Talk with your doctor about homocysteine risk factors and get them to order the test for you. Or, if you are in the US, you can order the test yourself through UltaLabs or other online lab test retailers. It’s a relatively inexpensive test.
Diet for CBS C699T or A360A:
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