Food & Nicotine Addictions: The Link Between Genetic Programming & Behavior

Tuesday, September 26, 2006 - 2:45pm

By John Messmer, MD

Recently, I saw a billboard for a fast-food restaurant chain that displayed a giant hamburger covered with various toppings. The caption below read: “Staring will just make you hungrier.” And it’s true; thinking about food increases our desire for it. For some of us, the lust for food can occupy much of our day. It’s kind of like a smoker’s “nicotine fit”, which makes sense. After all, for many people eating and smoking are similar cravings that produce similar pleasures.

The biology of addiction

Why can some people leave their favorite food on a plate when they’re full, while others feel compelled to snack after finishing a huge meal? Research studies demonstrate that this situation is similar to the problem smokers have when they cannot stop smoking—even when they’re faced with heart disease or crippling lung deterioration. In each instance, pleasure centers in our brains are stimulated that motivate us to seek more of the same pleasurable activity. Thus, we develop hunger to motivate us to seek food and are rewarded when we consume it (particularly calorie dense foods). For primitive humans, in order to eat they had to track and kill an animal or scrounge for edible plants. If there were no reward these difficult activities, our forebears might have died from lack of motivation.

At birth, babies seek food for the same reason. Much of our biology compels us to behave in ways that keep the species going. When we fulfill our biological drives, we are rewarded with pleasurable sensations. Unfortunately, biology does not always work to our long-term advantage. Along the way of evolution, we learned that fruits and grains left to ferment were even more pleasurable than the fresh stuff. Many plants contained compounds developed to deter pests but which stimulate the pleasure areas of our brains when we ingest them.

The interconnectedness of pleasure centers with eating and addictive chemicals may be the reason why overweight smokers continue to smoke while dieting. They often feel as though smoking helps them lose weight. In reality, smoking continues to stimulate the pleasure centers that are not being engaged by eating.

Feeding patterns may be caused by gene mutations

Studying primitive statues depicting women who would be considered obese today, anthropologists hypothesize that early humans had a very different idea of beauty than we do today. Being overweight once conferred a survival advantage when food was scarce. A few extra pounds increased the chance of reproduction, which is the essential biological requirement of our genes. Over time, changes or mutations in various genes may have passed on to some of us a defective approach to feeding. Brain nerve cells have receptors for various signaling chemicals or neurotransmitters. Different mutations change receptors or levels of neurotransmitters which can result in failure to feel full after a meal or cause us to feel anxiety or depression only relieved by eating.

Brain receptors influence eating and smoking

Recent studies have found endocannabinoid (EC) receptors in the brain. These EC receptors get their name from cannabis, the name for marijuana. Scientists suspected their existence by observing marijuana users. It is common knowledge that smoking marijuana causes “the munchies.” What purpose is served for us to have a marijuana brain receptor? The EC chemicals our brains quiet fear and anxiety—much like marijuana makes people care little about life’s worries.

Once scientists discovered that brain receptors were related to appetite, they set to work developing medications to aid people struggling with their weight. Although there are numerous brain chemicals involved in appetite, they focused on blocking the EC receptor in the brain with a drug called rimonabant, which is currently being tested. Rimonabant works to block the EC receptor, causing the opposite effect produced when marijuana stimulates it. It also reduces the pleasurable feelings experienced by nicotine addicts. However, because the causes of obesity are quite complex, rimonabant is no panacea. Just as stimulation of the EC receptor relieves anxiety, blocking it can cause anxiety in some people, which may limit its effectiveness.

Willpower still works

Food cravings and drug addictions are complex behaviors that will not be cured by one treatment for all. Even if rimonabant or other EC blockers are approved for use, they will not be for everyone. Just like drug addiction, food addiction can be managed through an understanding of the problem and learning to manage it one day at a time. We can deal with overeating triggers and develop a tolerance for just-enough food, while modifying our moods with healthy attitudes and activities rather than with food.