In recent years, scientists have made great advances in understanding important environmental causes of obesity. Although a person’s risk for obesity is influenced most heavily by behavioral choices, major efforts are now being directed toward assessing the interactions of genes and environment in the obesity epidemic.
What is Obesity?
Obesity is the result of a chronic energy imbalance (eating and drinking more calories than you burn through exercise and normal daily activities). Your body then stores these extra calories as fat.
In recent decades, obesity has reached epidemic proportions in populations whose environments offer an abundance of calorie-rich foods and few opportunities for physical activity. Obesity is a major health hazard worldwide and is associated with several common diseases such as diabetes, hypertension, heart disease and some cancers.
The “Thrifty Genotype” Hypothesis
A commonly quoted genetic explanation for the rapid rise in obesity is the mismatch between today’s environment and “energy-thrifty genes.” These “thrifty genes” multiplied in the past under different environmental conditions when food sources were rather unpredictable. In other words, according to the “thrifty genotype” hypothesis, the same genes that helped our ancestors survive occasional famines are now being challenged by environments in which food is abundant year round.
It has been argued that the “thrifty genotype” is just part of a wider spectrum of ways in which genes can favor fat accumulation in a given environment. These ways include:
- the drive to overeat (poor regulation of appetite)
- the tendency to be physically inactive
- a diminished ability to use dietary fats as fuel
- an enlarged, easily stimulated capacity to store body fat
Not all people living in countries with abundant food and reduced physical activity are or will become obese; nor will all obese people have the same body fat distribution or suffer the same health issues. The variation in how people respond to the same environmental conditions is an additional indication that genes play a role in the development of obesity. This is consistent with the theory that obesity results from genetic variation interacting with shifting environmental conditions.
Nutrigenomics and Nutrigenetics
According to the Genetics Society of America, “new research suggests that the genetic interaction with diet primarily determines variations in metabolic traits, such as body weight, as opposed to diet alone. This helps explain why some diets work better for some people than others, and suggests that future diets should be tailored to an individual’s genes.”
Nutritional genomics, referred to as nutrigenomics, is the study of how food and nutrition play a role in gene expression.
Nutritional genetics, known as nutrigenetics, focuses on a person’s genetic predisposition to respond a particular way to a given dietary nutrient.
Based on a study conducted by Pathway Genomics, 179 overweight California school employees showed significant weight loss success at the end of six months when taking a nutrigenetic test compared to employees who had previously tried to lose weight, under similar conditions, without a genetic test.
By gaining genetic insight about how an individual’s diet may impact his or her risk for disease, we will have the ability to make a stronger impact on patient health by personalizing diet and exercise recommendations to help treat each patient.
By providing a holisitic view of a patient’s health, Healthy Weight DNA Insight may help:
- Achieve a more desirable weight
- Prevent disease
- Improve energy levels
Genetics and Family History
Generally speaking, genes regulate how our bodies capture, store and release energy from food. Scientific evidence for a genetic basis for obesity comes from a variety of studies. Mostly, this evidence includes studies of resemblance and differences among family members, twins and adoptees.
The use of family history and genetics has made it easier to start reducing the effects of obesity in populations. Family history reflects genetic susceptibility and environmental exposures shared by close relatives. Health care practitioners can routinely collect family health history to help identify people at high risk of obesity-related disorders such as diabetes, cardiovascular diseases and some forms of cancer.
Even when someone has a genetic predisposition to obesity, environmental factors ultimately make you gain more weight. Obesity usually results from a combination of causes and contributing factors, including:
- Inactivity. If you’re not very active, you don’t burn as many calories. With a sedentary lifestyle, you can easily take in more calories every day than you burn off through exercise and normal daily activities.
- Unhealthy diet and eating habits. Having a diet that’s high in calories, eating fast food, skipping breakfast, consuming high-calorie drinks and eating oversized portions all contribute to weight gain.
- Family lifestyle. Family members tend to have similar eating, lifestyle and activity habits. If one or both of your parents are obese, your risk of being obese is increased.
- Quitting smoking. Quitting smoking is often associated with weight gain. And for some, it can lead to a weight gain of as much as several pounds a week for several months, which can result in obesity. In the long run, however, quitting smoking is still a greater benefit to your health than continuing to smoke.
- Pregnancy. During pregnancy a woman’s weight necessarily increases. Some women find this weight difficult to lose after the baby is born. This weight gain may contribute to the development of obesity in women.
- Lack of sleep. Not getting enough sleep at night can cause changes in hormones that increase your appetite. You may also crave foods high in calories and carbohydrates, which can contribute to weight gain.
- Certain medications. Some medications can lead to weight gain if you don’t compensate through diet or activity. These medications include some antidepressants, anti-seizure medications, diabetes medications, antipsychotic medications, steroids and beta blockers.
- Age. Obesity can occur at any age, even in young children. But as you age, hormonal changes and a less active lifestyle increase your risk of obesity. In addition, the amount of muscle in your body tends to decrease with age. This lower muscle mass leads to a decrease in metabolism. These changes also reduce calorie needs and can make it harder to keep off excess weight. If you don’t control what you eat as you age, you’ll likely gain weight.
- Social and economic issues. Certain social and economic issues may be linked to obesity. You may not have safe areas to exercise, you may not have been taught healthy ways of cooking, or you may not have money to buy healthier foods. In addition, the people you spend time with may influence your weight — you’re more likely to become obese if you have obese friends or relatives.
Even if you have a genetic predisposition to obesity (based on family history) or you have one or more of these risk factors, it doesn’t mean that you’re destined to become obese. You can counteract most risk factors through diet, physical activity and behavior changes.
If you have any concerns about your risk for obesity, please consult your doctor.
For more tips on weightloss and to hear Dr. Schumacher’s advice, visit our December blog post, “Winning the War on Weight Loss.”
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