Having read the two books mentioned in an earlier blog, I started to piece together some of my own biochemical jigsaw. For as long as I could remember, I had had an extreme hunger reaction, often getting so hungry that I felt clammy, nauseous, shaky and faint. I HAD to eat….and eat a LOT quickly to reverse of symptoms. Generally what worked was something fast acting….biscuits washed down with milk was a common solution. What I realised during the first of many diets, was that this wasn’t actually really “hunger”, being “empty” was a completely different feeling. What I had been reacting to was my blood sugar levels – (see the section on insulin) and I learned to avoid eating sweet things on their own – a biscuit after a meal didn’t have the same effect – as the spike and then plummet in blood sugar was avoided. But if I did succumb to cakes or chocolates at work, then I really had to keep going back for more….or suffer the unpleasant consequences. I could eat and eat and eat once I started….never seeming to tire of food and certainly never feeling full. One of the best moments about 7 weeks in to my sugar free journey was feeling full when there was still food on my plate – and I wasn’t stuffed to the gullet. (see the section on leptin).
So what makes us hungry? Why do we stop eating once we’ve started? This cycle is largely governed by hormones – the chemicals released by our bodies by certain stimuli, external or internal, that pass messages and trigger our behaviour – the biological basis of why we do things. One of the most surprising facts for me, is that some of the hormones involved in the appetite/hunger/satiety cycle are actually MADE in fat cells. As fat release from storage cells is the main source of our energy – our bodies have evolved to be very protective of fat stores. They are critical to our very survival – and in that light it’s no surprise that there are mechanisms within our bodies designed to lay down fat for times of need and to protect our fat stores. Women’s ability to ovulate, get pregnant and therefore the very survival of the species is totally dependent on us having a certain amount of fat. Puberty kicks in only when a set percentage of body fat is reached – and our obesity epidemic may be explaining why children are starting puberty younger and younger. Dancers, gymnasts and models who remain underweight, often miss their periods for months – only having their normal cycle return when they gain weight on stopping training. The way that messages are passed around the body is largely controlled by hormones – a brief description of the major players follows.
- Ghrelin, the most predominant “hunger hormone” we know of, is released by cells mostly within the stomach’s lining. Your stomach rumbling when empty? That’s ghrelin.
- Neuropeptide Y (NPY) is an extremely potent stimulator of feeding behavior. Found in the brain, it also takes part in circadian rhythms, sexual functioning, and anxiety responses. It is, in part, regulated by cortisol – the stress hormone.
- Leptin is synthesized within fat cells, and works as an “satiety factor” on the brain to dampen eating behavior while increasing energy expenditure. Leptin appears to act, at least in part, by inhibiting NPY synthesis and release in the brain. Leptin deficency is linked to anorexia nervosa as well as other disorders. Leptin is also affected by cortisol, decreases insulin production and increases insulin re-absorption – and has a role in insulin insensitivity. Excess insulin interferes with the bodies ability to “hear” leptin. Too much sugar – and we don’t feel full.
- Adiponectin, secreted by fat cells, helps regulate energy balance and the metabolism of sugars and fats, as well as increasing insulin sensitivity.
- Peptide YY (PYY) has been shown to slow digestion, suppress appetite, and significantly reduce food consumption.
- Cholecystokinin (CCK) is released in the duodenum in response to high-fat or high-protein meals. It signals the brain to produce a sense of fullness or satiety.
Other metabolic hormones:
- Insulin determines whether blood sugar gets used right away for immediate energy, or is alternatively stored as fat. Because fat is not simply a passive energy-storage site, but functions as an organ that produces important hormones itself, what we eat really does matter when it comes to losing weight and keeping it off. Insulin levels are directly impacted by our diets, particularly the ratio of carbohydrates to fiber, fat, and protein. Exercise lowers blood glucose levels as this can help to stimulate insulin production. Our bodies can become de-sensitised to insulin when high levels circulate in the body prompted by excess sugar – eventually leading to diabetes. When blood sugar is low, the body signals the stomach to produce hunger symptoms, and demand fuel. When blood sugar is high, there is plenty of fuel available, but no way for your body to use it, so your cells starve in spite of the banquet. Your body, in an effort to get fuel into the cells, again signals the stomach to produce hunger symptoms. Stop eating sugar – and you can reverse insulin resistance and get blow sugar levels under control.
- Thyroid hormones – the thyroid acts like a gas pedal in regulating your metabolism, but its relationship to weight gain is more indirect than generally believed.
- Stress hormones. Cortisol regulates energy by selecting the right type and amount of substrate (carbohydrate, fat or protein) that is needed by the body to meet the physiological demands that is placed upon it. Cortisol mobilizes energy by tapping into the body’s fat stores and moving it from one location to another, or delivering it to hungry tissues such as working muscle. Adrenal imbalance caused by excessive anxiety, stress, and cortisol production is typically at the top of the list when it comes to the correlation of unwanted weight (particularly belly fat) and hormonal imbalance. Sustained high cortisol levels can lead to intense cravings and binge eating. High cortisol production can throw off any or all of the other hormones in the body, major or minor, setting off a chain reaction that leaves your body in chronic crisis mode. The simple significance of this is that no diet will succeed if you are under tremendous stress, no matter what you do. Interventions to control excess cortisol, whether it is through exercise, relaxation techniques or changing your external stress will make an impact on other hormones key to your weight.
- Melatonin, the hormone that regulates the circadian rhythm, also factors into your hunger time-clock. Research shows that sleep deprivation throws off melatonin production, which in turn influences leptin and ghrelin production – sometimes up to 15% increases in the sleep deprived versus the well rested.
- Sex hormones – estrogen, progesterone, and testosterone. Adequate levels of estrogen seem to help in hunger regulation, simulating the soothing “full” or satiety effect of serotonin. As anyone familiar with premenstrual binges can attest, an imbalance in the ratio between estrogen and progesterone can trigger intense food cravings. Testosterone-deficiency, either poor nutrition or during perimenopause, will lead to difficulty building muscle mass. Testosterone production relies on adequate levels of cholesterol, the building block of all sex hormones and is why a low fat diet is not always to be recommended.
What is understood by endocrinologists is that there is no single hormonal factor in obesity – many of the hormones listed above are inter-linked and influenced not just by what we eat, but also our age, how we are sleeping and our stress levels. Interventions need to target more than just cutting calories. Get your insulin levels steady (cut out sugar), start to hear the “full” hormone leptin, get your cortisol levels under control (by exercise, relaxation techniques and environmental changes) and then get an early night!