What is GLP-1 dieting? How much weight is lost, and what happens when you stop?

GLP-1 dieting is a method that uses a medication similar to a gut hormone (GLP-1) involved in satiety, reducing food intake to lose weight.[1]In trials of obese individuals, weight decreased by 5–18%, but it was also found that weight tends to return when the medication is discontinued.[2][3]Effectiveness and safety have been confirmed primarily in obese individuals, and the same results cannot be assumed for people who wish to lose only a small amount of weight.[4].

Why does weight decrease?

GLP-1 is a hormone released from the gut after eating, and it is involved in blood sugar regulation and satiety.[1]The medication used in GLP-1 dieting mimics this hormone to create a state where hunger is less likely to occur.[1].

In other words, it is not a medication that directly dissolves fat. Weight decreases as a result of reduced food intake.

How much weight is lost? How should we interpret research figures?

In large trials, weight decreased by an average of 14.9–17.4% over 68 weeks.[4]For a person weighing 100 kg, that would be approximately 15 kg of weight loss.

However, the average weight of participants in this trial was 100–107 kg.[4]In actual clinical practice, the effect is somewhat smaller; a report in people without diabetes showed approximately 11% weight loss over 60 weeks.[2].

In a 2-year trial, the average 15.2% weight loss at the 104-week mark was maintained.[5]While continuing the medication, the lost weight tends to be maintained.[5].

Is GLP-1 dieting suitable for people who are not obese?

This is not yet clear. The 2-year trial mentioned above targeted individuals with a BMI (body mass index) of 30 or higher, or 27 or higher with weight-related diseases.[5].

Among the research we reviewed, we did not find large-scale studies examining use of GLP-1 for cosmetic purposes in non-obese individuals. It has also been noted as a limitation of these trials that participants were predominantly female and had low representation of non-white populations.[5].

We cannot say that the same proportion of efficacy and safety from the trials applies to people who want to lose "just a few more kilograms." This is an important premise to understand before treatment.

What are common side effects? Are there serious ones?

The most common are gastrointestinal symptoms such as nausea, diarrhea, and constipation.[2]In one trial, nausea occurred in 44% of the medication group and 16% of the placebo group.[2].

Most of these symptoms are mild and temporary, and are reported to be more common during the period when the medication dose is increased gradually.[5][6]For this reason, starting with a low dose and increasing gradually is standard practice.[7].

Rarely, pancreatitis (inflammation of the pancreas) and bowel obstruction have been reported.[1]A warning label is attached for people who have medullary thyroid carcinoma or multiple endocrine neoplasia type 2, either personally or in their family.[1]Regarding gallbladder disease, it is stated that further investigation is needed.[3].

Does weight return if you stop?

It tends to return. In a follow-up of a large trial, one year after stopping the medication, 68% of the lost weight had returned.[3].

In another trial, people who continued the medication experienced an average 17.4% weight loss, while those who stopped midway gained 6.9% of their body weight.[7]Before starting, it is important to think through how long you will continue and what you will do when you stop.

As food intake decreases, nutrient deficiency and loss of muscle and bone are also raised as concerns.[2][3]Protein intake and physical activity need to be considered alongside the medication.[2].

What should be confirmed in a consultation before starting?

You should confirm your current weight and body composition, any existing medical conditions and medications you are taking, any history of pancreatitis or gallbladder disease, thyroid disease history, and family history. Then, discuss with your doctor whether this approach suits your goals.

You should also ask at the beginning about how long you plan to continue and how you will maintain your weight after stopping. Whether GLP-1 dieting is right for you cannot be decided from an article alone, so it is most reliable to make a judgment after having a doctor assess your physical condition.