Sunday, August 15, 2010

Go to Health: Ghrelin and Leptin – the hunger hormones

There are many influences that govern what, when and how much we eat. Clearly our family of origin, habits and thinking play a big role in this, and so do the temptations of sweet, salty and rich foods in every store and restaurant. Most of us probably want to get in touch with our body’s signals that tell us when and how much to eat. Several hormones are constantly playing an unseen and important role in this. Ghrelin (the word comes from “ghre" in Proto-Indo-European languages meaning “grow") is made in the stomach and pancreas; it stimulates hunger. To pronounce this word, make ghrel rhyme with dwell, then add an ‘in’. Leptin (derived from the Greek word ‘leptos’ meaning thin) is formed mainly in fat tissue and inhibits

Ghrelin levels increase before meals and when blood sugar is low. Ghrelin stimulates hunger. The hormone circulates in the blood and affects areas of the brain that cause an increase in growth hormone and the dopamine reward area. The pleasurable aspects of food (and alcohol) are reinforced. Ghrelin has also been found to reinforce learning and memory (think of a hungry animal looking for clues to find food). Short sleep duration is associated with increased levels of ghrelin, increased hunger and obesity – so getting enough sleep is important to maintaining a normal weight.

Leptin is a hormone secreted mainly from fat cells – receptors are found in brain areas known to be important in regulating hunger, body temperature and energy expenditure. When an animal gains weight and has larger amounts of body fat, leptin levels rise. Normally, hunger and food intake go down, and body temperature rises. Leptin counteracts the effects of anandamide, a neurotransmitter that stimulates eating and binds to the same receptors as THC in marijuana. Anandamide makes food pleasurable, as does marijuana, while leptin signals the brain that the body has had enough to eat. A recent study in rats showed that animals fed a diet high in fructose became resistant to leptin, and gained more weight than animals on a diet with similar calories but without fructose. This study gives a clue to the rise of obesity in the US. It’s fine to eat fruit, but avoid sweetened drinks, especially if they contain fructose.

The ‘Appestat’ The regulation of appetite has been the subject of much recent research, primarily because of the marked increase in weight gain in our population. The hypothalamus in the brain is the main regulatory organ for appetite; it is influenced by ghrelin, leptin and many other hormones and neurotransmitters. Research indicates that it takes time for the brain to register a feeling of fullness after eating, possibly up to 20 minutes. People who eat rapidly, or are distracted by watching television, may eat more than they need, by ignoring and not waiting for the body’s signals of fullness. Foods that contain more water, fiber and/or protein have the greatest ability to promote feelings of fullness. Most vegetables, fruits and beans or animal foods fall into this category. Whole grain pasta, bread and cereal contain more fiber than foods with refined flour foods, and are 50% more filling. However, choosing healthy food when you are hungry, and confronted with foods like chocolate cake or cheeseburgers, takes considerable resolve! Carrying some nuts, fruit or dried fruit in your backpack or purse can help.

Self-knowledge There are many valuable ways to stay in touch with your body – meditation, conscious relaxation, mindful breathing, and slow walking, come to mind. Slow and conscious eating can also be a great help in staying in touch with your body’s need for the right amount of healthy food.
Sadja Greenwood, MD, MPH – back issues on this blog

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