Hunger is both a cause and a consequence of obesity and diabetes, and a problem with the hormone leptin is the main reason. During the entire time that insulin resistance is developing in your body, a second problem, leptin resistance, is developing in your brain. Whether one causes the other or they both develop at the same time doesn’t really matter. What matters is that problems with leptin lead to excess hunger, weight gain, and a slow metabolism.
Leptin is a hormone excreted by your fat cells that controls body fat, hunger, and metabolism. This hormone is being produced inside your fat cells. It orchestrates cortisone’s and adrenaline’s influence on your blood pressure, cholesterol, and blood sugar. It is primarily increased in two ways.
Over and over again each day, your brain monitors how much fat you have by how much leptin comes knocking at its door. Since fatter people have more leptin, their brains expect more leptin to reach the hypothalamus, the part of your brain that regulates hunger and metabolism. Likewise, slimmer people’s brains expect less leptin. Regardless of whether you’re heavyset or slender, your brain expects a certain amount of leptin from your fat cells. When you’re eating enough calories to maintain your weight, the amount of leptin in your blood is highly correlated with how much body fat you have. As you’ll read below the problems with leptin happen when you’re eating too few or too many calories.
The hypothalamus controls hormones and neurotransmitters that increase or decrease metabolism and hunger. If too much leptin reaches your hypothalamus, metabolism is increased and hunger is decreased. Unfortunately, if not enough leptin reaches the brain, metabolism is decreased and hunger is increased. In particular hunger for foods loaded with high glycemic carbs and saturated fats increases without enough leptin from not enough calories. This is the reason you start to crave ice cream and pizza after a few days on a diet!
If you start a diet today, you will lose body fat as you cut calories. However, with less body fat comes less leptin production. As a result, less leptin reaches the brain. As a consequence, hunger increases and metabolism decreases. On the other hand, what happens if you overeat? You gain body fat. And with a rise in body fat comes a rise in leptin. Hence leptin levels increase. As a result, your hunger goes down and your metabolism goes up. This explains why you are not so hungry after a large meal, not only for the remainder of the day, but for the next few days. And this also explains why after the initial bloat and water gain wears off, you really don’t gain much weight, if any, from one day of overfeeding.
In one study, men who were massively overfed carbohydrates gained a little over five ounces of fat per day max. Leptin is the scientific answer to what you’ve always known:
Leptin also explains the set-point theory, or the reason that people tend to stay the same weight no matter what. The body is hard-wired for survival. It does not know you’d rather have six-pack abs than survive an ice age.
So far, you’ve read about leptin behaving normally. The more leptin in the brain, the faster your metabolism and the less your hunger will be. However, being very overweight or diabetic makes leptin go haywire by causing leptin resistance. For the same reasons that you previously learned you were resistant to the hormone insulin when very overweight, you’re also resistant to leptin. It’s a direct consequence of excessive triglycerides created from excess body fat.
Years of overeating highly processed foods in large quantities without exercise made you fatter. The extra fat caused too much leptin to be excreted from your fat cells, bombarding your hypothalamus with too much of this hormone’s message to elevate metabolism and shut off hunger. This damaged the brain’s leptin receptors in the process. As a result, those receptors became numb to leptin’s orders. This is called leptin resistance, and it’s analogous to insulin resistance.
Leptin resistance doesn’t happen from just one big meal. It comes from the leptin created by gaining lots of weight. Take this example. Researchers from Jefferson Medical College overfed eight healthy individuals around fifty-five calories for every pound they weighed over twelve hours. Leptin rose 40% above normal and remained high until the next morning. The same researchers then overfed six normal men until they gained 10% of their body weight,. They then continued to overfeed them so they could maintain that weight for two weeks. By then, leptin had risen three-fold in all subjects. In short, their brains’ response to leptin was directly correlated with the percentage of body fat gained. So if you overeat in the short run, leptin will rise, elevate metabolism and decrease hunger, but drop before it contributes to leptin resistance.
However, if you gain a lot of fat, the extra leptin can certainly cause fat gain and boost hunger. Further, gaining muscle will add barely any leptin to your system. This study goes to show that you want enough leptin to keep your metabolic rate high, but not so much that it causes weight gain.
Leptin resistance can also occur after years of abuse to your metabolism in one or more of the following ways:
All of these contribute to leptin resistance by damaging the hypothalamus’s ability to detect the correct amount of leptin in the brain.
When anyone with insulin, leptin, and a certain degree of adrenaline resistance gets stressed, food cravings and overeating are almost inevitable. To understand why, you need to understand leptin’s opposite, Neuropeptide-Y (NPY).
You can think of NPY and leptin as friends sitting on a teeter-totter. When one is high, the other is low. NPY is the chief hunger signal in your brain. When NPY is high, you’re hungry. Stress elevates NPY and “overworks” either the left or right hemisphere of the brain.
When the right brain is stressed, serotonin, the neurotransmitter that fights anxiety, depression, sadness, and carb cravings, gets depleted. NPY goes up and leptin goes down. This all creates hunger from the high NPY, and carb cravings from the low serotonin. In short, you’ll get hunger for cookies and ice cream.
Subconsciously, the craving will serve to increase your sense of well-being, relieve some tension, and put you in a better mood by increasing serotonin. This won’t increase your ability to do work of course. However, it will make you feel better about getting back to work. Here is a summary.
When the left brain is stressed, the neurotransmitter dopamine gets depleted. Dopamine is responsible for concentration, motivation, and drive. It’s built from the amino acid tyrosine. Tyrosine is found in all sources of protein, but abundant in cheese.
So not surprisingly, an overworked person with left-brain stress will crave foods high in protein, fat, and salt. This is where hunger for pizza, burgers, and fries when stressed comes from.
Subconsciously, this overworked soul is looking for more motivation and focus to get back to work. Dopamine cravings are a desire to increase productivity, directly contributing to the bottom line, unlike serotonin cravings. Here is a summary.
But when you’re always stressed-out, it’s a different story…
To have be very overweight or diabetic is to have both leptin resistance and adrenaline resistance. This makes hunger for both types of cravings worst.
First, snacking on nachos or cheeseburgers under stress will not produce enough levodopa in the adrenals. They are fatigued after all. Even after eating a meal high in fat, salt, and protein, there will be a dopamine deficiency. Second, the leptin resistance will prevent enough leptin from entering the brain. Therefore, NPY will stay elevated, leaving the hunger signal turned on. In this case, you will remain stressed, tired, and hungry for high-calorie protein, fat, and salt foods. This is precisely where pizza, Mexican, Italian, and fast food cravings come from. The end result is that you will need to overeat to finally get enough dopamine and leptin in the brain to shut down NPY and feel energized and focused once again.
By then, the cost will have been too much – you’ll have already overeaten, gained weight, and your blood sugar will have spiked.
Likewise, when you’re leptin resistant and experiencing stress cravings for carbs and fat due to low serotonin, you will not be able to get enough leptin in the brain to shut down NPY before overeating on doughnuts, candy bars, or ice cream. Again, to finally feel relaxed and satisfied from eating, you’ll have eaten too much. You’re still hungry, irritable, and anxious despite eating. The high sugar snack solves nothing, but makes you fatter with higher blood sugar. As the stress continues to wear down your levels of serotonin and dopamine, you’ll become a carb-or salty-fat craving machine. This is where stress cravings come from.
Another way that leptin increases hunger is by increasing ghrelin. Ghrelin is the stomach hormone that gives you those hunger pangs, telling you to eat. Decreasing NPY also decreases ghrelin. Unfortunately, in diabetic or obese individuals, NPY and ghrelin are higher than normal. This means the physical and conscious feeling of hunger is stronger and longer lasting in diabetic and overweight people. Ghrelin also does not subside as quickly in diabetics and overweight people. This means they don’t receive the signal to stop eating as soon. So NPY in the brain is not lowered as soon, which increases the duration of the meal and the likelihood to overeat. This is one reason why determining hours before what you are going to eat, and measuring that amount through an already prepared meal, will go a long way in preventing you from overeating when you’re the most susceptible.
The above excerpt was adapted from my book, The New Diabetes Prescription.
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