In the ‘old days’ – really only up until 5 years ago! – when we had only moderately effective obesity medicines with 5% or maybe 10% weight loss, there wasn’t much reason for concern that weight loss could be too fast. The landscape has since changed dramatically, with new and emerging medicines demonstrating average weight loss in the 15-30% range, with such profound appetite reduction for some people that the weight comes off too quickly.
A recent Endocrine Society position statement on obesity science, research gaps and opportunities in pharmacotherapy discusses potential risks of weight loss that is too fast.
What are the risks of weight loss that is too fast?
- while weight loss of any cause decreases bone density, faster weight loss may result in greater bone loss
- muscle mass may deplete to a greater extent
- increased risk of gallstones
- increased risk of vitamin, mineral and protein deficiency
- increased risk of electrolyte imbalances
- increased risk of fatigue
How fast weight loss is too fast? As the position statement correctly points out, we don’t have data to give us a precise answer. While this answer should be individualized, prior publications (previously blogged here) suggest that weight loss faster than 1kg per week, or 5% per month may be too fast.
Most clinical trials of obesity medicines still take the approach of rapid dose titration, often mandated on a specific schedule. This is unacceptable for several reasons, one of which is that some people will lose weight too fast. Some trials allow flexibility in this scheduled approach; for trials that don’t, we sometimes end up needing to stop the treatment entirely, when the patient could have done quite well with maintaining a lower dose, or decreasing the treatment dose. Flexibility in dose titration needs to be the rule in clinical trials, not the exception. In the real world, flexible treatment is exactly how obesity medicines should be used: as per our Obesity Canada Pharmacotherapy Clinical Practice Guidelines (on which I’m the lead author), weight management medicines should be titrated as needed, as appropriate, and as tolerated for each individual to achieve treatment goals.
The position statement suggests that studies are needed looking at weight loss of up to 1% per week vs >1% per week to evaluate changes in body composition (muscle, fat, bone), physical function, metabolic health, mental health, energy levels, and overall wellbeing, to see if we can better pinpoint what rate of weight loss may be too fast, and what parameters may be affected. They also suggest that clinical trials with set targets (an example could be BMI <27) rather than aiming for maximum treated dose are critical (I wholeheartedly agree! – more on this blogged here).
BOTTOM LINE: Weight loss that is too fast with weight management medication comes with several risks. Obesity medicines are part of the ‘long game’ of treatment, and while some people will do just fine with the standard dose titration schedule, others will lose weight too fast. Studies of these medicines need to employ a flexible treatment approach, which reflects what we do in real life: titration as needed, as tolerated, and as appropriate to each person to achieve their individualized treatment goals.
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