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How does food impact our hormones?

Hormones are chemical messengers in the body that carry out a number of essential roles with one of their functions being to keep everything in balance through a process called homeostasis. You can think of them as your body’s thermostat: when the temperature gets too low, the thermostat will tell the heating to fire up; when the temperature gets too high, the thermostat will tell the air conditioning to kick in. In the same way that your thermostat keeps your house within a “healthy” temperature range, your hormones try to keep you working optimally by maintaining homeostasis in your body.

A group of these hormones control the use, storage and availability of nutrients in the body. In a healthy hormonal system, biochemical components in food trigger the secretion of these hormones into the bloodstream where they correct the shift in equilibrium caused by the influx of digested food. However, if you have hormonal dysfunction your body will secrete too much or not enough of the required hormones which has knock on effects to the systems they are trying to manage such as your metabolism, appetite, sleep cycles, growth, mood or stress. Even a small accumulation of visceral fat (the fat stored in and around your abdominal organs) is enough to promote hormone dysfunction. If you are eating too much or eat too many refined carbs or eat dietary stressors or have an unhealthy amount of body fat then the chances are you have hormone dysfunction to some degree or other and your hormones are in need of repair.

The endocrine system

The endocrine system is a chemical messenger system consisting of your hormones, the group of glands that secrete those hormones and the feedback loops which modulate hormone release. The major endocrine glands are the thyroid gland, pineal gland, pituitary gland, pancreas, adrenal gland, ovaries and testis however a number of other organs in the body are also involved in hormone production. The human body manufactures some fifty different hormones with a wide variety of these being produced by endocrine glands but we are going to focus on five key players that are critical in digestion: the pancreas; the adrenal glands; adipose tissue; the stomach; and the thyroid gland.

The pancreas (insulin and glucagon)

The pancreas is primarily responsible for blood sugar regulation through the production of two critical hormones: insulin (which acts to lower blood sugar) and glucagon (which acts to raise blood sugar). Rises in your blood sugar are detected by the pancreas which responds by releasing insulin into your bloodstream. The insulin travels through the blood telling the cells in your body to open up and let the glucose in. Once inside, the cells can convert glucose into energy or store it with any excess glucose being converted into glycogen and stored in the liver and muscles.

Glucagon is a hormone that works in reverse to insulin. When the pancreas detects that blood sugar levels are low then it starts to secrete glucagon into the bloodstream. The glucagon then tells the body to break down the energy stored in fat and convert stored liver glycogen (and if necessary, protein from your muscles) into glucose, trickling it into the bloodstream to provide you with energy and keep blood sugar levels normal[1].

If you have a healthy metabolism then your blood sugar levels rise moderately after a meal; not too much and not too fast. As the blood sugar levels increase, the pancreas dispatches just enough insulin to communicate to the cells exactly how much blood sugar they need to be stored. When your cells are insulin sensitive, they hear the insulin message and respond appropriately by pulling the blood sugar out of the bloodstream and storing it thereby returning the blood sugar to normal. Insulin sensitivity is indicative of a nice, normal, healthy relationship between the pancreas and most tissues in the body.

The trouble with insulin and glucagon is that they only operate within normal blood sugar levels and you can wear them down. If you are eating too many carbs then you will create an excess of blood glucose (once the cells and glycogen stores become full) which in turn will tilt you metabolism towards burning blood sugar instead of fat for energy. The pancreas tries to do its job by releasing more insulin to reduce the blood sugar, but the cells start to protect themselves to avoid the damage from being overfilled by becoming insulin resistant.

When your cells are insulin resistant, they lose their sensitivity to insulin’s message to store glucose and so the pancreas releases more insulin which further increases the cells resistance and your blood sugar levels continue to remain high. This cycle continues with the pancreas producing more and more insulin and the cells becoming more and more resistant. Eventually the blood sugar levels become toxically high and can cause oxidative stress, pancreatic problems, insulin failure and diabetes.

The other problem with insulin resistance is that glucagon cannot work when insulin levels are elevated and so you cannot stabilize falling blood sugar levels. If you are insulin resistant, after you eat a high carb meal your insulin levels will rise and stay high for a few hours but when you need to tap into your glycogen or fat stores for energy, your glucagon will not work thanks to elevated insulin levels. This leads to those all too familiar blood sugar lows and subsequent snacking that we have all experienced.

The adrenal gland (cortisol)

The adrenal gland is also in the digestive system and produces another important hormone called cortisol. Cortisol is associated with the fight-or-flight response and helps the body respond to stress by prompting glucagon to get to work and provide you with quick energy from glycogen stored in the liver or muscle tissues. There are a number of stressors that can trigger cortisol and release, including psychological stress, being chronically under slept, over exercising and prolonged periods of eating too little.

Cortisol helps you feel alert by mobilizing energy for activities and fire up your nervous system. It is at its highest level just before you wake up and then declines throughout the day helping you to relax before bed and sleep well. Cortisol follows a circadian rhythm that is controlled by the night-day cycle, so if you watch TV or play with your mobile phone late at night then your cortisol levels will remain artificially high making it hard to unwind.

Cutting calories from your diet is somewhat stressful for your body and may elevate cortisol levels, which will only add more stress to your already overstressed system. Chronically elevated cortisol impairs your glucose uptake from the bloodstream and enhances the breakdown of glycogen which leads to a build-up of glucose in the blood. This in turn can inhibit insulin secretion from the pancreas and lead to further insulin resistance which paradoxically makes it harder for you to lose weight.

But elevated cortisol levels can also contribute to weight gain by inducing stress-related overeating. When we have high levels of cortisol in your system stimulates the need for more glucose which can lead you to eating carb-dense, high GL foods to help temporarily reduce your stress but in the long-term increases you weight. And if all that wasn’t bad enough, elevated cortisol can mess with your normal thyroid function which results in a metabolic slowdown and will cause you to put on weight even if you are not overeating.

Adipose tissue (leptin)

The excess of glucose from your sugar dependent metabolism and build-up of triglycerides from fat accumulation pushes another hormone out of balance: leptin. Leptin is a hormone that is produced in your adipose (fat) tissue that regulates your energy levels both from a big picture and detail-oriented perspective. It signals to us whether we have enough energy available for the various activities of your day but also whether we have enough body fat stored for the harder times ahead.

Leptin is primarily secreted by fat cells in your adipose tissues and follows your normal daily cycle. When you wake up in the morning your leptin levels are low signaling that you need to eat. When you have finished eating your dinner, your leptin levels are high helping you feel full and satisfied. But leptin is also designed to help your body maintain its weight by regulating your energy balance and inhibiting hunger.

When leptin levels are between a certain threshold, it tells your brain that you have enough energy stored in fat cells for normal metabolic processes. If your body fat percentage increases, then your leptin levels will increase and if your body fat percentage decreases then your leptin levels with decrease. Your brain will then alter your food-seeking behaviors and activity levels appropriately. If your leptin levels are low, then your body will typically respond by doing less exercise, slowing your metabolism and eating more. This is why dieting can be so hard. After you have lost some weight, your leptin levels will drop and you get a double whammy of burning fewer calories and wanting to eat more calories.

But the real trouble starts when you overeat fats and carbohydrates. Your body is naturally pessimistic because of its ancestral hunter-gatherer wiring and likes to store fat for the rainy days when there is a food shortage. When your hormones are working normally, the leptin will tell your brain that you have acquired enough body fat and to eat less and move more. But excess triglycerides and glucose in the bloodstream start to impair your brains ability hear the leptin. The receptors in your brain and tissues become less sensitive to the leptin signals and so your body continues to your body continues thinking that you are too thin because it is a pessimist. This is leptin resistance.

Unfortunately, the signals from leptin are more powerful than your willpower so despite your best intentions if you are leptin resistant you will carry on eating more than you should. A hallmark of leptin resistance are those food cravings after dinner. And when you combine leptin resistance with insulin resistance, you end up in a cycle where your brain is telling your metabolism to slow down, do less exercise and eat more whilst your body is burning blood sugar over fat and accumulates triglycerides.

The stomach (ghrelin)

Leptin works in conjunction with a hormone called ghrelin. Ghrelin is termed the 'hunger hormone' because it stimulates appetite and increases food intake. It is produced and released mainly by the stomach where it circulates in the bloodstream and acts at the hypothalamus, an area of the brain crucial in the control of appetite. Ghrelin plays a big role in determining how quickly hunger comes back after we eat.

Ghrelin tends to follow the timing of your normal meal routines and is secreted just before we start eating to signal the need to begin a meal. Eating will reduce the concentration of ghrelin however it is most responsive to protein intake than carbohydrates and fats. So, if we eat high-carb or fatty meals then the hormonal system telling us that we have had enough to eat does not work as well. Ghrelin levels increase during dieting which may explain why diet-induced weight loss can be difficult to maintain. Ghrelin levels also tend to be higher in people who are lean although there is evidence to show that overweight people are more sensitive to ghrelin.

[1] Let’s just recap as it is easy to get confused with such similar sounding names: glucose is the body’s preferred energy source found in the bloodstream; glycogen is a stored form of glucose found in liver and muscles; and glucagon is the hormone that triggers the conversion of glycogen back into glucose.

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