Oh and of course, if there is any time you are going to have a low carb meal during the day, I recommend dinner

Putting your body into a catabolic state overnight is going to increase your lipolysis, vs a heavy carb meal with the resulting insulin spike will actually make you lipogenic for awhile and waste some of those 8 hrs

I choose free fat burning while you sleep

Tardy though I may be to this party, the Cap'n has some info to share!

(As an aside, remember that BMR is not fixed. It moves up or down based on a host of factors, including (perhaps especially) hormonal signaling.)

Nearly all regulation of BMR begins in the hypothalamus. Given that the hypothalamus produces all of the hormones that regulate the pituitary gland AND is the brain center most closely associated with hunger, thirst, satiation, biological clock, etc. It is a target for hormones that affect hunger or metabolism (e.g. cholecystokinin and vasoactive intestinal peptide) AND a producer of hormones that increase or decrease BR. With this in mind, here is a short list of hormone acting through, on, or because of the hypothalamus that regulate BMR.

(1) Somatostatin, Growth hormone releasing hormone (GHRH), and thyrotropin releasing hormone (TRH). These three hormones are produced in the hypothalamus. GHRH targets the somatotrophs of the anterior pituitary gland and leads to the release of growth hormone (GH). TRH targets the thyrotrophs of the anterior pituitary gland and leads to the release of thyroid stimulating hormone (TSH). GH acts directly on some tissues, indirectly on others (through intermediary molecules called insulin-like growth factors) to promote cell growth and metabolism. Given the growth connection, this hormone is a bit more important for metabolism in children than in adults, but is not trivial in adults. TSH, on the other hand, leads to the production of mainly thyroxine (T4) by the thyroid gland follicles. Note that of the monoamine thyroid hormones T3 and T4, T3 is the main actor but T4 is produced in bulk and converted to T3 inside target cells. Thyroxine promotes cellular metabolism in nearly every cell in the body (minus the thyroid itself, brain, spleen, testes, ovaries, and uterus). When it comes to promoting metabolism in the body, thyroxine is the heavy lifter, but note its production is preceded by TRH and TSH. Circling back to somatostatin, it is the OFF hormone for metabolism. It inhibits the production of both GH and TRH, slowing the activity of both of these metabolism stimulating hormones.

(2) Leptin -- Produced by our adipose (fat) tissue, this hormone targets the hypthalamus and increases metabolic rate. Note that the more fat you have the more leptin you produce. Thus, when you have a higher percentage of body fat your hypothalamus is essentially given a signal that says "you have large energy reserves; burn away!" On the other hand, less body fat leads to slower metabolism..."you have less reserve...better slow the burn to conserve!" This is a major reason it is harder to lost the last few pounds because your reduction in body fat creates a sort of metabolic drag.

(3) Digestive Hormones. Many hormones produced by the digestive system to regulate the process of digestion (especially the transition from gastric to intestinal activity) also affect metabolism via their effects on appetite. Cholecystokinin (CCK) which is produced in the duodenum and peptide YY which is produced in both the large and small intestines act as appetite suppressants as the digestive process proceeds and ghrelin which is produced in the stomach when empty and inactive increases appetite. These hormones influence metabolism via their affects on appetite.

(4) Sugar Regulating Hormones. The hormones that regulate blood sugar can potentially influence weight by increasing or decreasing the availability of sugar (glucose) for uptake as an energy source. Insulin gets beaten up here...I hate how people in MFP talk about "evil insulin." If you think insulin is bad, ask someone with T1DM (type I diabetes) about life without insulin. We NEED this hormone to keep our blood sugar in check. The issue with insulin is how much are you producing relative to exercise. If you are highly physically active, even if you gorge on carbs and spike your insulin, you'll see minimal weight gain...skeletal muscle and adipose tissue are the prime targets for insulin and the energy hog that is skeletal muscle will get more of that glucose for ATP synthesis if it is used regularly...weight gain linked to insulin becomes an issue when you are sedentary and your muscle isn't using the sugar...so insulin produces more fat uptake of sugar and energy storage. Bottom line -- insulin is a lovely, lovely hormone and we'd die without it. It creates issues for weight when you mismanage your own body. Note also that many people with T2DM (type II diabetes) end up LOSING weight...blood sugar is high but insulin insensitivity prevents them from accessing that energy, so their body starts relying more on protein and lipid metabolism to survive...hence weight loss.

Two other sugar-regulating hormones bear mention -- insulin's partner, glucagon (also produced by the pancreas) and cortisol (and its fellow glucocorticoids produced in the adrenal cortex). Glucagon increases blood sugar (mainly through causing the liver to release glucose stored as glycogen) as does cortisol (by enhancing non-carbohydrate cellular metabolism). If either of these are produced to excess, the result can be hyperglycemia which in time can lead to increased metabolism (due to extra available fuel) and weight gain.

Cortisol is insidious in that it is linked to stress. A certain amount of cortisol is released every day through a hypothalamus/pituitary pathway (corticotropin releasing hormone (CRH) from the hypothalamus and adrenocorticogropic hormone (ACTH) from the anterior pituitary) to stabilize blood sugar between meals. However, this same pathway can be excessively triggered during stress. When you combine the increased release of cortisol with the (usually) associated release of epinephrine and norepinephrine (adrenaline), the result is a large increase in blood sugar to support the body's stress response, up to and including a full-blown "fight-or-flight" response. The reality is, we evolved to deal with discrete stress...the leopard jumps at us, we run, assuming we survive, it's over. Modern stress is typically more chronic and as such can lead to increases in blood sugar that facilitate the development of both large waistlines and (eventually) T2DM when insulin is overproduced.

On the subject of muscle development, certainly hormones like GH and testosterone facilitate increasing muscle mass, especially during youth and puberty and especially in men. However, real changes in muscle mass are more about usage than hormonal signals and BMR. If we assume the simplified view that there are two basic skeletal muscle fiber types -- slow oxidative and fast glycolytic -- and we understand that muscle is a permanent tissue, so separate from senescence, loss of muscle mass is about atrophy rather than loss of cells, then it's all about exercise. Strength training promotes formation of larger, less durable fast glycolytic fibers. Provided adequate protein is available, strength training (and other anaerobic exercise) facilitates this transformation and mass increases. Endurance training facilitates the conversion of fibers to the slow oxidative type which are much more durable but smaller (containing less protein). Using myself as an example here, I've watched both my fat AND lean body mass drop in recent months...and that isn't a problem. My main form of exercise is running and I do minimal (though now increasing) strength training. Thus, the constant cardio-training has produced more slow fibers in my legs...hence muscle mass decreases as endurance rises. (Skeletal muscle presents the classic trade-off in mechanics...you can't be both highly durable and highly powerful...power sacrifices endurance and endurance sacrifices power.) Since my fitness goals revolve around long-distance running, this is cool with me. (Have you ever seen huge, muscly marathon winners? No! They don't (really can't) exist!) Bottom line -- any hormone that affects growth, blood sugar, or metabolism has the capacity to affect muscle mass, but real changes in muscle mass in adults are a function of exercise before hormones.

Hope this clears some things up! Hit me with any follow up questions you have...I'll be checking in again this evening.

Steve "Cap" Schenk

Haha - We just finished our Endocrinology block and while the basic principals seem easy, the fact that if you try to draw out an interaction diagram, all you see are lines going everywhere is one reason I am NOT going to be an endocrinologist.

Maybe Cardio

That's a pretty awesome bit of info there, Steve. Thanks!

And yes... I'd take cardiology over endocrinology any day :P Or for that matter, I'd take neuroscience over endocrine (which I have). Not that endocrine isn't interesting... just that you think you've got it only to find out that you really don't. It's not just hormone goes up, hormone goes down... /sigh

But I totally agree about learning basic principles first. You can get some good milage out of the basics.

Flow diagrams, huh? I like diagrams. Especially if they're colored I'd love to see a diagram or three.

Here is a sample flow diagram framework I use in class. It's not in color/no bells/no whistles. It's designed for students to sit in groups of 3 - 5 and, based on reading assignments, diagram all hormones linked to a particular process. This one is for the hypothalamic/pituitary axis and BMR.

Ok, something I remembered from Dr Oz ages ago (ugh, I don't really like him, but whatever :P)

Ghrelin? Does this exist and does it really regulate hunger levels?

I have not seen it brought up on these forums before, and admittedly never looked into it myself.

zactly. The only hunger abatement you get is when the baby is so big that your stomach is compressed and there's no physical room for food! Not to mention there's not one study that didn't result in the same amount of weight loss with a placebo and no it doesn't matter if it's injected or not. same results!