Many of us may know that our hunger is regulated by certain hormones: ghrelin and leptin. These two hormones perform opposite actions, that is, ghrelin increases appitite, whereas leptin decreases it. They are two big players in the regulation of hunger and, therefore, play an important role in our body weight.
Ghrelin, also known as hunger hormone, is a hormone produced by ghrelin cells found mainly in stomach and duodenum but also in jejunum, lungs, pancreatic islets, gonads, adrenal cortex, placenta and kidneys. It has recently been shown that ghrelin is produced locally in the brain. Ghrelin is thought to signal hunger to the brain.
Functions of ghrelin –
The following are important functions of ghrelin:
- The level of ghreilin is expected to increase if a person is under-eating and decrease if the person is over-eating, a mechanism that has its roots in the hypothalamus in the brain. Normally, ghrelin levels go up dramatically before we eat; this signals hunger. They then go down for about three hours after the meal. Therefore, ghrelin levels play a big role in determining how quickly hunger comes back after we eat.
- Ghrelin also stimulates the release of growth hormone from the pituitary gland, which unlike ghrelin itself breaks down fat tissue and causes the build-up of muscle.
- Ghrelin is also important to the brain’s ability to adapt to new environments and learn new things – a process called neurotrophy. It has been found that ghrelin enters the hippocampus of the brain from the blood and alters the connections between nerves and cells to enhance learning and memory. Therefore, learning is most effective during the day, when the stomach is empty, because ghrelin levels are higher on empty stomach.
- A recent research has concluded that the ghrelin hormone not only stimulates the brain giving rise to an increase in appetite but also favors accumulation of visceral fatty tissue, located in the abdominal area, considered to be the most harmful. Ghrelin can show itself in acylated or non-acylated form. Previously, it was thought that only the acylated form was active in the process of weight increase, but many studies point to both forms of hormone being biologically functional.
Factors affecting ghrelin production –
The following factors affect plasma ghrelin concentration -
- Food – Post-prandial suppression of ghrelin occurs after ingesting meals of mixed macronutrient contents. It appears that three classes of macronutrients viz. carbohydrates, proteins and fats can suppress plasma ghrelin but with varying efficacy. The hypothesis that increases in insulin after ingestion of food cause the postprandial reduction in ghrelin levels has received an especially large amount of attention. It seems clear that an increase in insulin after ingestion is not required for meal-related ghrelin suppression.
- Exercise - According to a new study, a vigorous 60-minute workout on a treadmill affects the release of ghrelin, while 90 minutes of weight lifting affects its release. Taken together, the research shows that aerobic exercise is better at suppressing appetite than non-aerobic. The researchers observed that the changes were short term for both types of exercise, lasting about two hours, including the time spent exercising. Ghrelin comes in two forms, acylated and non-acylated. The researchers measured acylated ghrelin, also called active ghrelin, because it can cross the blood-brain barrier and reach the appetite center in the brain. Long-term exercise programs do not influence ghrelin levels directly. Instead, exercise acts through changes in body mass to modify ghrelin levels. One study found that females did increase acylated ghrelin levels in response to an exercise program, regardless of whether or not a steady energy balance was maintained with increased food intake. No such changes were observed in males.
- Stress – It has been found by the researchers that chronic stress increases ghrelin release sending signals of hunger to the brain, which is the reason behind food-reward behaviors in individuals under chronic stress. This is the result of direct interaction of ghrelin on dopaminergic neurons in the brain’s ventral temental area, which is known to be associated with pleasure and reward behaviors. Alternately, it has also been noted that behaviors associated with depression and anxiety decrease when ghrelin levels rise. However, an unfortunate side-effect of such behaviors is an increase in food intake with resultant increase in body weight. Nevertheless, some researchers suggest that blocking the body’s response to ghrelin signals might be one way to control body weight by decreasing food intake and increasing energy expenditure.
- Sleep – The researchers have found that people suffering from a lack of sleep had 16 percent less leptin and nearly 15 percent more ghrelin than those, who were slept well. These days chronic sleep restriction is common and food is widely available. So, changes in appetite regulatory hormones with sleep curtailment may contribute to obesity.
- Circadian rhythm - The level of ghrelin increases during the time of day from midnight to dawn in thinner or normal weight people. Whenever there is disturbance of circadian rhythm such as in people working in shift duties, it affects ghrelin levels. Ghrelin levels reflect release in a circadian rhythm, which can be interrupted by exposure to light at night, thereby causing obesity in shift workers. It has also been suggested that there is a flaw in the circadian rhythm of obese people, adversely affecting the normal release of ghrelin.
- Aging- Ghrelin plasma concentration increases with age. And this may be one of the contributory factors giving rise to a tendency of weight gain as people age.
- Obesity gene - The persons, who carry a version of common obesity gene, don't feel full after eating and take in extra calories. The researchers have discovered that the variant of the FTO gene in question, which one in six individuals carry, leads to higher levels of ghrelin involved in mediating appetite and the body's response to food. There is a lot of work that's been done on the mechanism of FTO in animals, but one has to be careful about applying those lessons to people. The full story of FTO remains to be uncovered.
Ghrelin and addictive behaviors –
There is enough evidence suggesting an association of ghrelin and obesity. As it is well known, the plasma ghrelin levels are enhanced under conditions of physiological stress. And, recently, it has been suggested that ghrelin plays an important role in stress-induced food-reward behavior. In addition, chronic stress or atypical depression has often demonstrated to correlate with an increase in ingestion of caloric dense comfort foods, which have been implicated as one of the major contributors to the increased prevalence of obesity. Therefore, the reward-related eating due to ghrelin may reveal itself as an important factor in the development of addiction to certain foods, similar to its involvement in the dependence to drugs of abuse, including alcohol.
The findings of a new study show that ghrelin may be involved in addictive behaviors and brain reward. It may be that common mechanisms in the brain underlie different forms of addictive behaviors, including compulsive overeating, pathological gambling, and drug dependence and alcoholism. These finding may help to explain the co-morbidity of different addictive behaviors and compulsive over-eating.
Ghrelin and diabetes –
Ghrelin, a peptide hormone from stomach, is also able to modify glucose and insulin metabolism. Studies have shown that ghrelin, long considered a key player in obesity, may take a major role in maintaining the balance between insulin and glucose and development of diabetes.
How to regulate ghrelin concentration –
The following are some important tips for regulating ghrelin in the body:
Eat at regular times – It has been found that ghrelin is influenced by heaviest meal of the day. Studies show that it is more important to eat at regularly scheduled times than how many times we eat in a day. By doing so, we are able to have a better control over our hunger throughout day. For example, if a person normally takes a heavy lunch at 1:00 pm but due to a reason decides to take a pre-lunch at 11:00 am, it is much more likely that the person will feel hungry again at 1:00 pm. Therefore, by eating at regularly scheduled times, we develop a pattern of hunger, over which we have a short-term control.
Avoid conditioned response to stress- As it is quite evident that people habitually reach for comfort foods when under stress. So, it matters most how successfully we can handle our stress. When confronted with stress, we should learn to take recourse to habits such as taking a small walk or doing some deep breathing so as to reduce overall stress. Such small activities will give us a handle over our hunger hormones.
Sleep well – Sleep plays a major role in controlling our hunger hormones. Studies show time and time again that those who sleep adequately weigh the least, whereas those who sleep the least, weigh the most.
Exercise - Exercise may be the most important aspect in controlling your hunger hormones over the long-term. It has been found that resistance training helps to make cells more sensitive to both insulin and leptin, allowing the signals of these hormones to be more powerfully exerted in the body at lower concentrations. The long-term fat loss programs show that leptin levels will drop with weight loss, showing that cells develop increased sensitivity to leptin something that diet alone cannot do without exercise.
Eat more fiber - Studies have shown that higher fiber intakes help to suppress ghrelin levels. By consistently eating higher fiber foods (think vegetables), you have a way of controlling these powerful hunger-inducing hormones.
The bottom-line –
It is evidently clear that ghrelin - the hunger hormone- plays a significant role in the regulation of hunger, which in its turn is influenced by so many factors. It is equally significant that these entire factors can also be managed with persistent efforts. Since plasma ghrelin level in our body effects us in many adverse ways, it becomes prudent for us to learn to manage it efficiently.