Originally Posted by Ntombi
Yes, we need these studies. Not everyone understands the role of insulin on weight, and not nearly enough people with medical training understand how looking beyond calorie intake can be crucial.
You're absolutely right, Ntombi.
I think most people believe we know more about how the human body functions than current research has actually established -- which is *why* research continues looking into things that the average person believes are settled points. The issue of brain chemistry and food is NOT well understood in humans. The neurotransmitter function of a catecholamine called "dopamine" stimulates a variety of physiological activities in humans that make the human response to food about more than just energy management and/or hormonal response. Dopamine is activated in humans by *pleasure* -- sugar, drugs, sex -- things that make you *feel* good stimulate increased dopamine activity. The sight or smell of *pleasing* food raises the serum insulin level in some humans, (partly) in response to the function of dopamine. And we don't *really* understand why. At this time, a lot of hormone research is done simply to establish *what* is happening inside the human body. Researchers are trying to establish what physiologically occurs under different conditions because they honestly don't know.
For example, two of the most significant regulators of human bodyfat were *discovered* during my lifetime: leptin function was identified in humans in the mid-1990s, and beta-3 adrenergic receptors were isolated in humans in the mid-1980s. Leptin choreographs a comprehensive series of hormonal, enzymatic, and neurotransmitter operations that regulate the level of stored human bodyfat. Beta-3 adrenergic receptors orchestrate levels of fat release from storage and also the rate at which skeletal muscle consumes energy. Both of these discoveries were made when researchers looked into phenomena that the average person probably believes is already well established or even obvious.
With leptin, researchers examined whether obese mice, who ate more than healthy-weight mice, were *hungry*. So they took the mouse brains apart to examine the hunger centers, and this examination (eventually) led to the discovery of leptin. With beta-3 receptors, researchers examined whether bodyfat release is stimulated by hormones. That seems kind of obvious, right? Researchers used drugs to *block* the major fat release hormone receptors in study subjects and then examined whether those subjects would/could still burn bodyfat as fuel. The subjects did continue to burn bodyfat and this examination (eventually) led to the discovery of beta-3 receptors.
The two primary enzymes in the human body that regulate fat storage are "lipoprotein lipase" (LPL) and "acylation-stimulating protein" (ASP). ASP wasn't discovered until the 1980s, but LPL was well-known and was thought to be the key (only) fat storage enzyme. So researchers did something that probably seemed obvious at the time, they manipulated the genes of test rodents and studied whether rodents who were born without LPL could still store fat. The test rodents were still able to store fat and this discovery eventually identified ASP -- and rodents who are born without ASP can't store fat, so the discovery of ASP vastly expanded our understanding of bodyfat regulation in mammals.
The human biochemical response to food is not just about insulin. It's not just about hormones, at all. Our current level of biophysical knowledge suggests that bodyweight/bodyfat regulation in humans is primarily about brain function -- the way that key signals in the brain control the function of hormones AND neurotransmitters AND enzymes AND a vast array of biochemical reactions that we may not yet know exist. Without having read the details of this study, I can't comment on what the researchers are actually *doing* but I do know that research into the functions of known hormones can be extremely fruitful -- especially when examined in the context of brain function -- even if the studies seem to be asking for answers to questions that most people believe have already been settled.
We don't really know *why* the human brain responds to food stimuli the way it does -- humans are quite different from other mammals in this respect, and those differences can't be adequately explained at this time. For example, the past couple of decades of research suggest that humans are a bit more complicated than other mammals, in that human bodyweight regulation may be as significantly influenced by environmental factors as by biological factors. Human bodyfat levels are higher in what researchers call "obesogenic environments" in a way that doesn't directly correspond to strictly biological factors. This probably seems like an obvious question: Do humans who have readily-available food eat more food than people for whom food is scarce? But it *isn't* obvious because other mammals respond to food scarcity by eating more and respond to food abundance by eating less -- the lack of food leads to overeating behavior that stores energy for future use at times when food may not be available. But there seems to be a cognitive element that makes this behavior different in humans.
For example, members of the same family who live in industrialized nations accumulate more bodyfat than their direct, genetic relatives that live in developing nations, even though the family members who live in industrialized nations typically continue eating the same basic foods and recipes as their relatives who live in the developing home nation. Human populations that live in food-rich environments have significantly higher levels of obesity than human populations that live in areas with more food scarcity, but *why* this happens is a question that biological research can't fully address. The biological and physiological theories of bodyweight/bodyfat regulation are currently being looked at alongside behavioral and environmental theories.
Basically, the current research looks at the way that human bodyweight is controlled by internal, biological factors AND is also heavily influenced by environmental stimuli and cultural behavior patterns. And all of these issues are about *how* the human brain operates, which is still an open question. Environmental food stimuli and cultural patterns seem to lead to food behavior that increases bodyweight/bodyfat but the *reasons* that this happens in humans is not clearly understood. Just because this research is looking at insulin and human brain chemistry, that doesn't necessarily mean it's *only* looking at blood insulin levels and things of that nature. So we don't know what the research might eventually lead to.