18.5 Factors That Influence Weight Loss and Weight Gain

In general, weight loss results from a negative energy balance while weight gain results from a positive energy balance. However, weight is one limited measurement of changes happening within the body, and weight loss or weight gain is more complicated than how many calories a person consumes and what their body uses. A person’s body weight will fluctuate day-to-day—even hour-to-hour—based on various factors including hormones, hydration or dehydration, and food intake. Further, weight cycling—repeated periods of losing and regaining weight, sometimes referred to as “yo-yo dieting”—is actually associated with weight gain and obesity, as well as many other risk factors (Dulloo et al., 2015; Montani, Schutz, & Dulloo, 2015). This indicates that long-term, more gradual adjustments to behaviors may not only be more sustainable, but also can mitigate multiple risks associated with repeated changes in weight or weight cycling.

Prevalence of obesity in the United States has increased over the past several decades (Brown, et al., 2016) with most research pointing to two main causes: changes in nutritional habits and decreased physical activity. However, many other factors can influence weight on an individual and population level. The following table—though far from comprehensive—lists some of these predictive factors.

Table: Some of the Predictive Factors Associated with Obesity (Gill, 2011)

Sleep debt can significantly influence metabolism through related hormones, and feeling tired can decrease the likelihood of physical activity (McAllister et al., 2009). Stress can influence weight by altering appetites; acute or short-term stressors can lead to appetite suppression, while chronic stressors can lead to increased appetite and changes in food preferences (Torres & Nowson, 2007). Chronic stressors can include things like experiencing ongoing discrimination, poverty or a stressful living environment, or long-term illness or fulfilling a caregiver role for an ill family member. Some of the most commonly prescribed pharmaceutical drugs—including antidepressants, hypertension drugs, antihistamines, birth control, and anti-inflammatory drugs—have also been associated with weight gain (Leslie, Hankey, & Lean, 2007).

Researchers studying thousands of pairs of twins have identified that genetic factors contribute significantly to individual differences in BMI (Maes, Neale, & Eaves, 1997), and the variations in microorganisms in our intestines in-part dictate how the body uses consumed calories, which can also influence body weight (Nieuwdorp et al., 2014). Proximity to convenience stores and limited park space is associated with obesity rates (Ohri-Vachaspati et al., 2015), which disproportionately impacts people from marginalized identities (Rummo et al., 2015; Abercrombie et al., 2008). Research has also shown that an individual is more likely to become obese if a spouse, sibling, or friend becomes obese (Christakis & Fowler, 2007), which means it appears to spread through social connections.

All in all, a wide variety of factors are at play in determining weight gain and obesity rates in an individual and across populations.