Chang Woock Lee, B.A.
Do you remember Popeye the Sailor, the cartoon and animation character with massive forearms and a smoking pipe in his mouth? He usually shows a calm and gentle demeanor, but when necessary, especially to protect Olive Oyl, the love of his life, from his archrival Bluto, he suddenly turns into a hyperactive action hero with superhuman strength by eating his magic food, a can of spinach.
What is this strength-giving magic food all about? Is there any element or property in spinach which is associated with muscular strength? The original creator of Popeye chose spinach as the magic food based on its vitamin A content (not iron as previously believed by many people), and he just thought eating spinach and vegetables would make children healthy. However, since vitamin A alone is unlikely to make you strong, 
the spinach story has been regarded as pure fiction until some light was shed on spinach recently.
The USDA has found that spinach has a very high concentration of the micronutrient betaine, a biomolecule that affects the synthesis of creatine, which is associated with strength and muscle gains. Betaine is obtained not only from dietary intake, it is also synthesized in our bodies from another important micronutrient, choline. Choline is an essential component of all cell membranes and participates in many physiological processes including reactions that lower cardiovascular risk. Choline deficiency causes fatty liver, muscle damage, cognitive dysfunction, and birth defects. Perhaps more important to Popeye, choline is a backbone of acetylcholine, a neurotransmitter that relays a nerve signal from the brain to muscles. Nerves and muscles are not directly connected. There is a gap between the two tissues, and it is acetylcholine that travels from the nerve through the gap to the muscle, carrying the message (nerve signal) from the brain to activate muscle so that contraction and force generation can occur. Acetylcholine availability and muscle contraction clearly depend on choline.
Our laboratory’s recent data support this idea. We analyzed the effect of choline consumption on muscle response to 12 weeks of resistance training in 50~69 year old adults and found that low choline intake has a negative effect on strength (maximum bench press + leg press weight) gains. Those who consumed 
an adequate amount of choline (based on current Adequate Intake (AI) values) gained more than double the strength compared with those with a lower intake. These preliminary results suggest that inadequate choline consumption may result in reduction of acetylcholine between nerves and muscles, negatively affecting force generation and strength gains. However, it is unclear whether a higher than adequate level of choline intake induces more force production and/or strength gains. Also unclear is whether the choline intake should vary with the level of physical activity. Our laboratory will try to answer these questions.
So, what do you think? Given the relationships between creatine, betaine, choline, and acetylcholine, doesn’t it sound like Popeye’s strength gain with spinach might have some truth to it?
- Foods rich in choline include beef/chicken liver, egg yolk, wheat germ, bacon, dried soybeans, and pork
- Foods rich in betaine include wheat bran, wheat germ, spinach, pretzels, shrimp, whole-wheat bread, and whole-grain cereals
References
- Zeisel SH and da Costa KA. Choline: an essential nutrient for public health. Nutrition Reviews. 2009; 67(11):615-23. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2782876/pdf/nihms102541.pdf
- Jäger R, Purpura M, and Kingsley M. Phospholipids and sports performance. J Int Soc Sports Nutr. 2007;4:5. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1997116/pdf/1550-2783-4-5.pdf