I had a visit recently with a very nice patient. She is 65 years old, very cooperative with medical advice, and overall a very motivated patient. Her BMI puts her in a category of moderate obesity. She has multiple medical problems including diabetes, high-cholesterol and hypertension. She asked me why it is that she cannot lose weight even though she eats healthy. I was delighted at her question and spent the next ten minutes explaining the medical basis for weight loss struggles and the different options available for safe and effective weight loss (including the use of medication). She listened attentively but in the end was adamant against using medications. Here is a patient who is willing to take multiple medications to treat the fruits of obesity (hypertension, diabetes, high cholesterol) but is against using the same strategy to the root cause of her problems. But she is not alone! A lot of people fail to lose weight or keep it off because of a lack of understanding of the science behind why we struggle.
Research is shedding more light on the biological basis of eating behavior
There are several hormones involved in controlling appetite and food intake. They accomplish this by activating brain centers that control hunger and satiety. The brain system involved in food intake and energy expenditure are very complex. They can be divided into the homeostatic and hedonic (reward) networks.
The homeostatic center found in the brainstem and the hypothalamus. Its main function is to gather information from hormones and nerve signals relating to hunger and satiety. It then transmits this information to the hedonic or reward areas of the brain. The homeostatic system is driven mostly by our need for energy to maintain balance.
On the other hand, the hedonic system is driven largely by perceived reward-value of food. It operates through release of dopamine, the feel-good neurotransmitter. Dopamine is released when we engage in things that give us pleasure such as eating foods we crave or engaging in sexual activity. It boosts mood, motivation, attention and helps to regulate movement, learning, and emotional responses. It initiates behavior based on the anticipated reward value of a stimulus or signal. Studies show greater activation of the hedonic system with food that is highly palatable such as high-sugar, high-salt and high-fat foods. The hedonic system can override the homeostatic system making it possible to continue to eat past satiation if the food is of high reward value.
The information from the hedonic center is transmitted to the prefrontal cortex. The prefrontal cortex integrates all the complex information and is connected to other areas of the cortex involved in planning and execution.
When we are hungry, the stomach releases high levels of hunger hormone called ghrelin. This activates the hunger center in the brain, and we feel hungry. On the other hand, after eating, several hormones made in the gut including GLP-1 and many others, activate satiety centers in the brain to make us feel full. There is also a hormone called leptin made by fat cells. Leptin stimulates areas of the brain that mediate satiety and make us feel full.
Several changes take place in how these hormones and neural signals work when we lose weight. For one the level of leptin falls as we los weight since leptin is made by fat cells. The fall in leptin leads to decrease in satiation. This makes it hard to feel satisfied with food. On the other hand, there is a rise in ghrelin level leading to increased hunger. The net result is increase in wave of hunger especially for foods with high reward potential such as sugar, salt and high fat foods. The reward reinforces the need for these foods. This system served our ancestors well when food was scarce. This was necessary for the survival of the human species and works with high fidelity.
This is why it’s such a struggle to lose weight and keep it off!
Weight loss unleashes very strong biological forces that drive up hunger, decrease satisfaction food and make us crave energy rich foods. This invariably leads to weight regain. Overcoming these strong forces, require a multi-pillar approach. An approach that includes the right eating plan (not dieting), activity, behavior training and medication management. For some surgery may even be needed.
Unfortunately, the prevailing view of weight loss struggle is that it is primarily a behavior failure. If you just push back at the table, you will be fine. This thinking continues to keep majority of people who can be effectively treated from seeking and getting the help they need.
If you or someone you know is dealing with excess body weight and struggling to lose weight, it is advisable to seek the help of a professional with interest and experience in obesity medicine. It could make all the difference.