In this video, we're going to examine energy balance and food intake versus energy output. So, remember that the potential energy that is found in the chemical bonds of the molecules we consume, when we break those bonds, the energy released from the food must equal the total energy output. So the intake refers to how much energy we liberate through the chemical process of oxidation when we break those chemical bonds down. While energy output is taking into account about 60% of the energy that is released from that chemical bond is lost as heat. So it's not usable energy. The remaining 40% energy is the usable energy that we either use to do work and we talked about transport, chemical and mechanical work that is primarily going to be driven by ATP. And anything in excess is going to be stored as fat or glycogen. So if energy intake equals energy output, then the overall weight of the individual is going to be stable. However, if there's an imbalance, this can associate with weight gain or weight loss. So if input or intake is higher than output, weight will be gained. If however output is higher than intake, then there's going to be weight loss. So the heat that we generate is not totally useless. It's useless to do work but it is useful in order to maintain body temperature. So it warms the tissues and the blood helping us to maintain that homeostatic body temperature. And by achieving this higher body temperature, the rates of diffusion as well as the rates of chemical reactions are going to occur more swiftly and efficiently. So when we examine obesity, so there's excessive input versus output, the body mass index is going to be elevated. So, how do we calculate the body mass index? Well, it's going to be your weight in pounds, not in kilograms. And we're going to multiply that number by 705. And then basically divide by the square of your height in inches. So, somebody whose BMI is between 25 to 30 is considered overweight. Anybody over 30 is considered obese. And this can increase your risk factors for atherosclerosis, type 2 diabetes, hypertension, heart disease, as well as osteoarthritis. So there's more mass impacting your joints, especially your knees. So today, there are more adults and children that are overweight um relative to 20 years ago. So this has a large part to diet lack of activity. So how do we regulate food intake? Now of course there's a little bit of detail here. So there are key parts of the brain that sort of register food intake and these three critical areas are known as the arcuate nucleus or the arc, the lateral hypothalamic area and the ventromedial nucleus of the hypothalamus. So two very important regions are in the hypothalamus itself. And these neurons are capable of releasing peptide hormones that influence our feeding behavior. So for example, the ARC they can secrete two peptide hormones, one neuropeptide Y and a goody related peptides, both of which actually enhance your appetite so you're more hungry. There are another class of ARC neurons. Uh they secrete a hormone called pro-opio melanocortin or pomc. Uh and then the second one is cocaine or empmphetamine regulated transcript or cart. And both of these help to suppress appetite. The point being here without going into the specifics is there are specific neuro hormones that can influence feeding behavior by enhancing your appetite or by suppressing your appetite. So your feeding behavior and your hunger are regulated by neural signals from your GI tract. So the entic nervous system is pretty complicated. uh you also have chemical signals in the blood to indicate energy levels. There are specific hormones and to a lesser extent your body temperature and psychological factors can influence how much food you intake. So a lot of this regulation is going to happen through specialized receptors like thermo receptors or chemoceptors. So thermmoore receptors detect body temperature. Cheo receptors look for specific solutes that are in the blood. So there are both shortterm and long-term regulators of food intake. So let's look at shortterm factors. And we're going to break this down into neural versus chemical versus hormones. So there are neural signals from the GI tract. So in case a meal is of high protein content, this is going to increase aerant veagal signals. So these are sensory neural signals, parasympathetic because it's veagal. Um then there's also distension of elements of the GI tract that the vagus nerve will send or will receive and send to the hunger centers of the brain. Nutrient signals. Well, if there's increased nutrient levels in the blood, doesn't mean you need it means you don't need to eat anymore. So, that can suppress eating. Rising levels of glucose, elevated levels of amino acid, elevated levels of fatty acids. So, all of these are telling you that you have nutrients available and you don't need to seek out additional sources. There are hormonal signals. So we've talked about insulin, right, which kicks in when you are hyperglycemic. That's going to suppress hunger, the GI tract hormone, choleiccystokinine or CCK, you know, when you're when food is already in your belly, right? There's that distension, you're releasing this particular hormone to indicate, hey, I don't need to eat anymore. Uh glucagon and epinephrine on the other other side of the table will stimulate hunger. So glucagon remember is the hormone that kicks in when you are hypoglycemic that leads to gluconneogenesis and glycogenolyis. So they kind of kick in in the postabsorbative state indicating hey I haven't had a meal in a while. And then there's the hormone ghrein from the stomach that is going to stimulate the appetite with levels that are peaking just prior to meal time. So when you're kind of anticipating the meal, you become hungry. So what are some of the long-term regulators of food intake? So a lot of this we'll focus again on specific hormones and in this case I want to focus on the hormone leptin. So leptin is a hormone that is secreted by atapost tissue specifically the fat cells in response to an increase in body fat mass. So it is an indicator of how much energy the total energy that is stored in fat tissue. So this is a specific hormone that protects us against weight loss when we are nutritionally deprived and it has effects on those ARC neurons in the hypothalamus to suppress neuropeptide Y. Remember neuropeptide Y was the neuro hormone that stimulated or enhanced the appetite. So while it suppresses the secretion of neuropeptide Y, it promotes those appetite suppressor signals like the cart peptides. Now when you have rising levels of leptin, this can lead to some weight loss. Although you would think that, oh well, why don't I stimulate leptin secretion, if you have higher levels of leptin in obese patients, eventually those obese patients generate resistance to those leptin levels. So the main function of this leptin hormone is to prevent excessive weight loss during periods of nutritional deficiency. So it's again there to help maintain homeostasis. So here we have a flowchart of both the shortterm and long-term controls. So we have physical changes like the distension of the GI tract. We have chemical changes as detected by the presence of glucose, amino acids and fatty acids. We have hormonal signals that impact the GI tract. We have hormonal signals like ghrein, glucagon, epinephrine that also ultimately regulate the secretion of hormones that can enhance or suppress appetite. With regards to long-term controls, we have insulin from the pancreas and leptin that have effect on the arc nucleus to either enhance or suppress appetite based on unique hormone signals. But there are additional factors that can regulate food intake. We mentioned temperature earlier. The cold tends to activate hunger, right? Because as your body temperature drops, your body realizes, well, an increase in food allows me to break those molecules down and produce that byproduct of heat. Stress has an effect on food intake. So during periods of excessive stress you increase the secretion of the stress hormone cortisol which causes more glucose to actually be released into the bloodstream. So in order to have more glucose you would enhance the sort of appetite and so you have your binge eating for example during this period so you have resources to release that glucose. uh psychological factors can have an impact on food intake. There's actually links to certain viral infections. So, adenoirus infections can trigger an increase in food intake, uh sleep deprivation. And lastly, and there's a lot of research coming out on this now, is the actual composition of gut bacteria. So the species and subspecies and strains of bacteria that have seated the GI tract largely the large intestine and the metabolites they produce can actually have a systemic effect on individuals. So if you look at for example the bacterial gut composition of um in the large intestine of somebody who's physically fit, it is vastly different from somebody who's obese. And so there is such a thing now as fecal transplants where you can seed the gut bacteria from somebody who is much more healthy with somebody who is not so much so.