Amped Training

The body's overall metabolic status is controlled by a master hormone called leptin. It also happens to be upstream of just about every process in the body that is related to metabolic function. In other words, having a normalized amount of leptin is something you want.

Leptin signaling is strongly linked to body fat levels, as well as to calorie intake. If you're carrying a decent amount of body fat and eat well, you do not have to particularly worry about this. On the other hand, if you're on a contest diet of 1000 cals per day and have crazy low levels of fat, then you're likely near bottomed out.

This has interesting implications. Centrally speaking, leptin is linked to a whole bunch of neurochemical mess in the brain. It's downstream of the dopamine pathway, which is responsible for things like pleasure-reward feedback. This might well implicate it in eating disorders. The hormones that control appetite also hang around this area. Again, no shock.

Thyroid, androgen, and adrenal output are all modulated by leptin as well. Which means that if you diet too hard, too long, you'll basically “crash”. The body appears to have an equilibrium point where it “wants” to be, in terms of body mass and composition, which is referred to as the setpoint. Going below the setpoint, along with chronic underfeeding, is what causes these problems.

We can take a few things away from this. Firstly, someone that's above his or her setpoint doesn't have to worry so much about the partitioning issue I mentioned before. There's plenty of leptin signaling going on, assuming a sane calorie deficit is in place, and proper strength training can help preserve muscle tissue.

Secondly, starvation diets are not a good idea. At least, over the long term. There's been quite a buzz about the phenomenon of so-called “metabolic damage”. Now, insofar as I know, which admittedly is not an infallible answer, the only way to truly damage the metabolism is to physically or chemically do something to the thyroid gland that causes it to stop functioning. The down-regulation of metabolism, the “crash”, has been shown in research to be limited to about 30% or so of baseline, and is easily undone by raising calories for a few weeks. There's nothing permanent about it, again barring actual damage to the thyroid gland (admittedly, not uncommon in women).

Now, applied properly, leptin-crushing low calories can be used. However this requires periodic increases in calories, and especially carbohydrate intake, called a refeed. Refeeds will vary in composition, and strictly defined they are simply periods of over-feeding. However, carb-based refeeds are the preference in many instances, due to the fact that glucose uptake by fat cells is the source of leptin signaling. Carb-based refeeds can span anywhere from 2g/kg to 16g/kg of carb intake, although the higher end of that is generally not a requirement. For most purposes, 2-7g/kg is likely plenty. In the research, intervals of less than 5 hours have been pretty useless for increasing leptin, so that's something to take into account also. This ties into the concept of cyclic dieting, which I'll cover a little more later.