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Around this time last year, a colleague shared a newly published research study titled “Sex Differences in the Efficacy of Glucagon‐Like Peptide‐1 Receptor Agonists for Weight Reduction: A Systematic Review and Meta‐Analysis.” I rolled my eyes. Great, another weight loss study that shows that males lose more weight due to their higher levels of testosterone, faster metabolisms due to having more muscle, etc. Do we really have to keep doing research on this topic?
Yet to my surprise, the results said just the opposite. In fact, when researchers looked across 13 different GLP-1 studies, they found that females achieved more weight loss than males.
It brings up a good point. Men and women’s bodies are different; we tend to gain weight differently and lose weight differently. We also experience different external factors and pressures to look or move a certain way. For these reasons, I wanted to explore what GLP-1s can mean for women’s health, starting with their effect on body composition.
Before we continue, let’s ground ourselves on three important terms: body composition, BMI and body shape.
Body composition refers to the ratios of body fat, muscle, organs, bone, and water within the body, which play a crucial role in assessing health and fitness. When stepping on a standard weight scale, we're presented with a single figure—our total body weight, which fails to differentiate between the aforementioned muscle, fat, organs, bone and water weight. This is where body composition comes in, offering insight into clinically significant proportions: body fat and muscle mass.
A healthy body composition is often characterized by a lower percentage of body fat and a higher percentage of muscle, with women naturally carrying higher body fat than men. Higher body fat—especially around the abdomen—is clinically linked to insulin resistance, high cholesterol, and inflammation, even in people who are “normal weight” or have a “healthy body mass index (BMI).”
That’s why it's important to distinguish body composition from BMI. Although BMI is a widely used metric in healthcare, it only looks at weight relative to height, without considering the muscle:fat ratio. Two people could have the same BMI but vastly different body compositions, and vastly different risk factors. For example, Uar Bernard, a defensive tackle for the Philadelphia Eagles, is 6’4’’, weighs 306 pounds, and would be considered obese with a BMI of 37.2, yet he only has 6% body fat.
Body composition and BMI are also separate from body shape. Women commonly identify as having an apple, pear, hourglass, or rectangle shape based on the Body Shape Assessment Scale, but body shape is largely determined by genetics and cannot be changed (despite what your favorite fitness influencer might have you believe). However, body composition can be influenced by adjustments to exercise, diet, and overall lifestyle.