The researchers from Maastricht University, The Netherlands, and KU Leuven, Belgium, also found that different types of fiber offer different benefits, suggesting that the industry should not focus solely on the amount of fiber consumed, but on the right fiber for the right person and the right stage of treatment.
“We propose that dietary fiber could play an important role in improving long-term treatment success, helping to manage gastrointestinal side effects, and potentially reducing weight regain when GLP-1 therapy is discontinued,” co-author Dr. Paul de Vos, a professor of sustainable foods and health at Maastricht University, told NutraIngredients.
Fiber as a standalone tool for weight management
The rise of GLP-1 medications has reshaped the dietary supplement industry, shifting the focus from traditional weight management solutions to companion products designed to manage side effects.
Indeed, data from market research firm SPINS suggests that sales for weight management products declined by 3% in the year leading up to August 2025, while Amazon sales for the same period dropped by 14%. At the same time, sales for products designed to help manage the side effects of GLP-1 medications have grown, with sales for digestive supplements up by 52%.
Fiber is widely used in both GLP-1 companion products and traditional weight management solutions because of its diverse functional properties. Glucomannan, inulin and psyllium are particularly common in weight management products, with the authors of the review highlighting one study which found a combination of these fibers led to a 4-5 kg reduction in body weight over eight weeks, compared with 3 kg in the placebo group.
These fibers have different mechanisms of action. For example, while fibers such as glucomannan and psyllium work by absorbing water and increasing the volume and viscosity of food in the stomach, helping people feel fuller for longer, inulin is fermented by gut microbes, producing short chain fatty acids (SCFAs) that stimulate the body’s own GLP-1 production and sending satiety signals to the brain.
However, the researchers state that GLP-1 drugs are substantially more potent, typically inducing a loss of 10-15% of total body weight.
“The reason is that pharmaceutical GLP-1 therapies are specifically designed to overcome the body’s natural limitations,” Dr. de Vos said. “Native GLP-1 has a half-life of only about 2-3 minutes before it is rapidly broken down, whereas drugs such as semaglutide have a half-life of approximately one week. This allows sustained receptor activation and much stronger effects on appetite, food intake and body weight.”
Managing side effects and supporting weight rebound
Side effects are one of the most common reasons that people stop taking GLP-1 drugs, with research published in RAND Health Quarterly suggesting that around half experience nausea, one third experience diarrhea and a fifth experience vomiting. Constipation is also a common issue.
Fiber has emerged as a promising strategy to help relieve some of these effects, but Dr. de Vos says the type of fiber is more important than the amount.
“I do not think we should focus solely on the amount of fiber consumed,” he said. “A recommendation such as ‘eat 30 grams of fiber per day’ is too simplistic. The biological effects depend strongly on the structure and function of the fiber. Some highly targeted fibers can selectively stimulate beneficial microbial species and their metabolites at relatively low doses and may therefore be highly effective despite being consumed in small quantities.”
During dose escalation, well-tolerated fibers that support bowel regularity, such as psyllium, may help manage gastrointestinal side effects, the review states. While in later maintenance or tapering phases, more fermentable fibers that stimulate endogenous GLP-1 production and support a healthy microbiota, such as inulin, may become increasingly important.
Certain fibers could therefore not only support the gut microbiome, but also address a common concern for GLP-1 users—weight regain—with research suggesting that, on average, users regain two-thirds of the weight they lost within 12 months of stopping the medication.
However, Dr. de Vos says clinical studies specifically designed to identify the optimal fiber type, dose, and timing during GLP-1 therapy are still lacking, representing an important area for future research.
“Although definitive clinical evidence is still lacking, we believe there are strong biological reasons to expect that targeted dietary fibers could support GLP-1 therapy in several ways,” he said. “As illustrated in our conceptual framework, we envision dietary fiber not as an alternative to GLP-1 therapy, but as a complementary tool that can be integrated throughout the treatment journey.”
Source: Advances in Nutrition. doi: 10.1016/j.advnut.2026.100647. “Dietary Fiber and Glucagon-Like Peptide-1 Receptor Agonists in Obesity Management: Converging Mechanisms, Interactions, and Strategies for Durable Weight Control.” Authors: Y. Wang, et al.
