Weight loss guaranteed! But what impact on your diet? A review of GLP-1 and GIP/GLP-1 interventions

By Hugo Francisco de SouzaReviewed by Susha Cheriyedath, M.Sc.Jul 29 2024

In a recent review published in the journal Obesity Pillars, a team of researchers collate and narratively review the literature on the dietary impacts of obesity or type 2 diabetes (T2D) patients undergoing glucagon-like peptide receptor agonists (GLP-1RAs) or glucose-dependent insulinotropic polypeptide/glucagon-like peptide receptor agonists (GIP/GLP-1RAs) clinical interventions.

Their findings highlight a significant shortage of available information, with only a limited amount of previously published studies meeting their review inclusion criteria. Furthermore, while these interventions achieve notable reductions in total caloric intakes (16-39%), dietary composition is rarely scientifically evaluated in receptor agonist studies. The authors recommend future studies to assess the protein and essential micronutrient intake change following GLP-1 or GIP/GLP-1 interventions and include a registered dietitian nutritionist (RDN) in the expert team.

Review: Dietary intake by patients taking GLP-1 and dual GIP/GLP-1 receptor agonists: A narrative review and discussion of research needs. Image Credit: Caroline Ruda / Shutterstock

Background

Obesity, clinically defined as a body mass index (BMI) over 35 kg/m², is an alarming public health condition. The World Health Organization (WHO) estimates that 16% of the global adult population suffers from the condition, with this prevalence highest in developed countries such as the United States (US; prevalence = 42%). Obesity is associated with clinically significant comorbidities, with studies revealing an increased risk of type 2 diabetes (T2D), cancers, cardiovascular diseases (CVDs), physical disabilities, and mortality.

Numerous nutritional, behavioral, physical, pharmacological, and surgical interventions have been developed to help obesity patients lose weight. The cutting-edge pharmacological interventions involve receptor agonists that increase insulin production, reduce glucagon secretions, and modulate dietary cravings. Glucagon-like peptide receptor agonists (GLP-1RAs) and glucose-dependent insulinotropic polypeptide/glucagon-like peptide receptor agonists (GIP/GLP-1RAs) are two popularly prescribed pharmacological interventions, given their unprecedented efficacy in achieving long-term weight reductions in obesity and T2D patients.

However, the paper highlights that indiscriminate weight loss may not always be a good thing, given the vital roles of proteins in maintaining muscle health and micronutrients (vitamins and minerals) in general somatic functioning. Unfortunately, despite substantial evidence for the weight-reducing benefits of receptor agonists, only a handful of studies investigate the role of these drugs on dietary intake.

About the study

The present narrative review aims to elucidate the role of GLP-1 or GIP/GLP-1 RA interventions on the dietary intake of obesity or T2D patients. Specifically, the authors investigated

1. The implementation of dietary interventions,
2. The methodologies used to quantify dietary intake,
3. Changes in dietary intake before and after the clinical RA interventions (or compare patients undergoing the intervention with those that are not),
4. Gaps in nutritional care among these patients.

Data for the study was collected from online scientific repositories using a customized keyword search strategy. Studies were included if they:

1. Were published in English,
2. Included either T2D or obesity patients and their dietary intakes,
3. Patient outcomes were measured and reported. Data collection comprised dietary intake reports, assessment methodologies, participant appetite, food preferences, and duration of dietary intake.

Study findings

Only ten studies met the review criteria and were included in the present narrative. Of these, eight compared the dietary parameters of T2D or obesity patients (receiving RA interventions) against placebos, while the remaining two compared patients receiving RA interventions to those who received nutritional/dietary counseling without pharmacological intake.

In interventions involving RA versus placebo, dietary intake was reduced by between 16% and 39% in the former cohort. In contrast, RA versus counseling interventions failed to report statistically significant dietary intake reductions. Notably, only one study employed the ‘gold standard’ of dietary intake measurement – the 24-hour dietary recall. The other studies employed variations of a standardized test meal to evaluate dietary intake.

Only two of the ten included studies reported the participation of a registered dietitian nutritionist (RDN) in the expert team. Evaluations of the impacts of GLP-1 or GIP/GLP-1 on dietary intake revealed that these interventions caused patients to shift their preference from a high-carb/high-fat diet to one comprising low-fat and no-sweet foods (reductions of up to 35%). Protein intake was observed to decrease by 17.1%. No studies measured changes in micronutrient (vitamins and minerals) intake as a consequence of RA interventions.

Conclusions and recommendations for future studies

The present narrative review investigates the dietary changes associated with GLP-1 or GIP/GLP-1 RA interventions in obesity or T2D patients. Study findings highlight that these drugs predominantly encourage patients to reduce their fat and sweet food intake, reducing total caloric intake by 16-39%.

Unfortunately, these findings also reveal research gaps across multiple axes. Firstly, only 10 studies met the inclusion criteria, highlighting the need for additional research across different populations, regions, and ethnicities. Secondly, a standardization of dietary intake measures is required, preferably the gold standard of the 24-hour dietary recall test. Thirdly, studies should include an RDN in both study design and implementation. Fourthly, given the importance of proteins and micronutrients in human health, these nutrients should explicitly be included in future evaluations of dietary intake.