|MadSci Network: Neuroscience|
Aloha, Kiriana, Thank you for asking such an interesting question. First I think I need to say a few words about nutrition and 'junk food.' I am a nutritionist at the University of Hawai`i at Manoa and teach many students each year in our introductory nutrition course. I find it difficult to use the term 'junk food' because I don't believe that there really is such a thing (yes, it's OK to eat a candy bar now/then...and french fries occasionally are just fine). There can be 'junk diets' because of choice and/or availibility of food. In such a diet, there may be too little of some nutrients (such as the vitamins, minerals, protein) or too much of some nutrients (such as vitamins, etc.) OR too much of some and too little of others...it is a question of balance. Now, on to your question. As you probably already know, the myelin sheath is a fatty substance around the 'limbs' (or processes) that sprout off of nerve cell bodies, mainly in the brain, but also in the spinal cord. The myelin sheath acts sort of like an insulator to keep messages from short-circuiting from one nerve pathway to another. Since the myelin sheath is made up mainly of fatty tissue, mothers or caretakers need to take particular care with the food that they feed infants and small children to make sure that they get enough fat in their diets. Did you know that human breast milk contains about 55% of its energy in the form of fat?! That is a very high-fat diet. What 'Mother Nature' is telling us is that infants need a lot of fat...partially to help the infant's body complete the development of the myelin sheath. Babies are born with an incompletely developed nervous system, so fat in the diet is really important, especially for the first 2-3 years of life. Now, I don't think any nutritionist, myself included, would recommend a diet of 'junk food' (whatever that means) for an infant (breast milk for the first 6 months is the recommendation). But, what about a less-than-perfect diet for older children, adolescents and adults. Will that affect the myelin sheath? Once the sheath is formed, the body will do what it can to maintain that sheath. Also, your brain is quite well protected from outside influences. Since it is essential to life, isn't this the way the body should be designed?...if you were doing the designing? Thus, some fat in the diet is used to keep the myelin sheath healthy. When the sheath starts to deteriorate, like in the disease multiple sclerosis, all kinds of strange things begin to happen to a person's ability to function. However, there is little/no evidence that diet plays any major role in the development of multiple sclerosis. We think that something goes wrong with the body's recognizing itself, in multiple sclerosis...and the body begins to destroy its own myelin sheath. As a last comment, a nutritionally balanced and varied diet, with enough energy to allow growth is what we recommended. What that means in terms of foods (we don't eat nutrients, really) is choosing well from an eating guide like the Food Guide Pyramid and eating according to when your body tells you to eat...when you're hungry...and stopping when your body tells you it has had enough. For a growing, active young person, that allows for occasional treat foods that may be high in energy and even high in fat (like candy bars, french fries, chips, ice cream, etc.).
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