Lifestyle Influences

Key Points

• Increased caloric intake is related in part to "portion distortion," linked to eating away from home.

• Smoking cessation is associated with weight gain of 4 to 5 kg (on average).

• Many antidepressants, neuroleptics, and anticonvulsants are associated with weight gain.

• Decreased overall physical activity (not just "exercise") is a major factor associated with the increasing prevalence of overweight and obesity.

As mentioned, obesity develops when caloric intake exceeds caloric expenditure against a background of genetic influences. The chief determinants of energy imbalance are lifestyle factors. Individual total energy requirements depend on the basal metabolic rate (BMR), thermic effect of food, and energy needed for the da/ s physical activities. The chief determinant of BMR is the amount of lean body mass, which can be difficult to increase. Some data indicate that the thermic effect of food (amount of energy needed to absorb, digest, and assimilate nutrients) is lower in obese persons than in lean subjects, but this difference is quite small. Physical activity (exercise and activity throughout the day) is the most variable component of energy expenditure. The major reasons for weight gain are therefore excessive calorie intake and decreased overall physical activity.

Caloric Intake

Over the past 40 years, the tendency in the U.S. population has been to consume more calories needed; per-capita consumption of calories increased from 2220 kcal in 1970 to 2680 kcal in 1997 (Putnam, 2000). Some of this increase is related to increased portion size; a normal portion in 1970 is much less than a normal portion in 2010. This "portion distortion" has been linked to people eating more away from home. The typically larger restaurant portion size has been adopted as the inhome standard as well (Foreyt and Poston, 2002).

Energy density also plays a role. Satiety helps determine food intake and is largely determined by the volume and weight of food consumed. Foods that are high in caloric content for a given volume lead to excessive calorie intake. This includes fat and highly processed foods such as sugar and other refined carbohydrates that are high in energy density. Per-capita consumption of sugar has greatly increased at the same time as the increasing prevalence of obesity.

The frequency of meals may play a small role. Eating smaller meals more frequently is associated with less overweight. Large meals are associated with more insulin release. This might be a mechanism whereby meal size influences weight gain.

Activity Changes

Decreased energy expenditure may play a greater role in the development of obesity than increased caloric intake. In the United States a progressive decrease in energy expenditure has coincided with the increase in calorie consumption (Foreyt and Poston, 2002). The amount of exercise has not changed much over the past few decades, so most of the decrease in physical activity energy expenditure has occurred in daily physical activities, not exercise.

Smoking Cessation

Often cited by smokers as a reason to continue smoking, stopping cigarette smoking does lead to weight gain. The average weight gain is 4 to 5 kg (~9-11 lb) over months (Flegal et al., 1995). Typically, the person gains 1 to 2 kg (~2-4 lb) in the first few weeks after cessation (Bray, 2002). Approximately 10% of people gain 10 kg (22 lb) or more.


A number of medications are associated with weight gain, including antidepressants, antipsychotics, anticonvulsants, and hypoglycemic agents. Tricyclic antidepressants, mono-amine oxidase inhibitors, and mirtazapine are the anti-depressants most likely to cause weight gain. Of the more common selective serotonin reuptake inhibitors (SSRIs), paroxetine is most likely to be associated with weight gain, although individual effects vary. Many neuroleptics can lead to weight gain. Phenothiazines and haloperidol, as well as some newer agents such as clozapine and olanzapine, tend to increase weight. Among anticonvulsants, valproic acid and gabapentin have been most closely tied to weight gain. Lamotrigine is thought to be weight neutral, whereas topi-ramate may actually promote weight loss. Insulin, as well as oral hypoglycemics that increase production or release of insulin, promote weight gain. It should be noted that met-formin, which increases insulin sensitivity, is associated with modest weight loss and may ameliorate the weight gain from other hypoglycemics. Chronic systemic steroid use can cause a cushingoid type of obesity.

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