Q: Like a lot of other people, my New Year's resolution was to lose weight. I started a high-protein, low-carbohydrate diet earlier this month, and I am losing weight. But I've noticed that my mood has taken a nosedive since I started eating this way. Am I imagining it or could the two things be related?

Dr. Wright: You're not imagining it. I'm sure you've heard the phrase "fat and happy." Well, it's not just folklore. The same carbs that make you fat (and contribute to diabetes and other problems) also make you happy. It's simple science: Carbs allow more of the amino acid L-tryptophan to penetrate your brain. The L-tryptophan triggers your brain to make more serotonin, and the serotonin makes you feel happier. It's as simple as that! But if you're following a low-carb diet, it's possible that not enough L-tryptophan will penetrate your brain, and you could wind up depressed.

So if you get depressed but don't want to eat more carbs, the solution can be as simple as taking supplemental tryptophan so there's more of it to penetrate the brain. Take either 1,500 milligrams twice daily or, if that makes you drowsy (which is rare but possible), take all 3,000 milligrams at bedtime. It'll pull you out of any high-protein diet depression you may have. Just make sure not to take it when you're eating protein. It's best to take tryptophan with whatever small amount of carbohydrates you do eat.

You might also want to take a small quantity of (over-the-counter) lithium, 5 milligrams, twice daily. Lithium "catalyses" one of the first steps in tryptophan metabolism, moving it more rapidly and effectively down the "metabolic pathways" toward serotonin. And even though low-dose lithium is quite safe, you can make it even safer by including essential fatty acids and vitamin E in your daily program. I always recommend that anyone taking lithium also take a teaspoonful or two of flaxseed oil (or other essential fatty acid) along with 400IU of vitamin E (as mixed tocopherols) each day.