December 19, 2025, 11:41 am | Read time: 5 minutes
They are considered the miracle drugs of our time: GLP-1 medications such as semaglutide and tirzepatide promise not only weight loss but also better blood sugar levels, reduced inflammation, kidney protection, and even heart benefits. But what of this has actually been proven so far? Which patients benefit the most from GLP-1-based therapies, and which new patient groups can hope–an internationally recognized metabolism expert explains on FITBOOK.
Few German researchers know the clinical study landscape and mechanisms of GLP-1-based medications as well as Prof. Dr. med. Norbert Stefan. At the University of Tübingen, the endocrinologist and diabetologist has been researching for many years, along with others, how fatty liver, type 2 diabetes, inflammation, and cardiometabolic risks are interconnected. His research group is among the leading centers worldwide seeking to understand how modern therapies can slow these processes. In the first part of the FITBOOK interview, we discuss which patients benefit the most from semaglutide and similar drugs–and which new patient groups can hope.
»Eighty Percent of GLP-1 Benefits in Diabetes Treatment
FITBOOK: Mr. Stefan, if we set aside all the headlines and hype: What do GLP-1 therapies scientifically achieve in your view–and why are they now considered a medical breakthrough for people with severe metabolic diseases?
Prof. Dr. med. Norbert Stefan: “GLP-1-based medications were developed for the treatment of type 2 diabetes, and I still see their benefit at eighty percent in this area. We now have about 20 years of experience–initially with older preparations, today with more modern agents like semaglutide or tirzepatide. The main benefit lies in improved blood sugar control in mostly overweight patients with type 2 diabetes–often within the first week of therapy, even before weight reduction begins.
“These drugs slow gastric emptying and promote insulin production, reducing glucose spikes. They are particularly effective for patients who can no longer be adequately managed with oral antidiabetics and are facing the decision to start insulin therapy. In these cases, GLP-1 analogs offer a valuable alternative with a significantly lower rate of hypoglycemia.”
»Benefits for People with Existing Cardiovascular Diseases
What benefits beyond pure diabetes treatment are now sufficiently well-proven by studies in your view?
“In addition to blood sugar regulation, GLP-1 analogs also show cardiovascular benefits. The SELECT study on semaglutide, for example, demonstrated that overweight patients with existing cardiovascular diseases benefit from therapy with semaglutide in terms of survival and reduction of recurrent events. Remarkably, the positive effect was observed independently of initial weight and weight loss–an indication of weight-independent, likely anti-inflammatory, mechanisms. Similar results have been found for the agents dulaglutide and tirzepatide.”
»Another Promising Application Area
“Another promising application area is the protection of kidney function. Although these medications are not yet approved in this context, studies in people with type 2 diabetes and chronic kidney disease already show cardiovascular and renal benefits.”
Prof. Dr. med. Norbert Stefan is an endocrinologist and diabetologist and holds the chair of clinical-experimental diabetology at the University Hospital Tübingen. He also heads the department of “Pathophysiology of Prediabetes” at the Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich. He has collaborated with manufacturers of GLP-1-based preparations, mostly in the context of scientific lecture events.
“Data Show That the Medications Can Improve Liver Inflammation and Fibrosis”
What other medical applications are currently being discussed or researched?
“A much-discussed new application area is the treatment of fatty liver hepatitis MASH (metabolic dysfunction-associated steatohepatitis, ed.) with fibrosis stages 2 and 3. In the U.S., semaglutide is already approved for this, while the approval process is still ongoing in Europe. The current data show that the medications can improve both liver inflammation and fibrosis.
There are also initial indications of potential benefits in heart failure. And research is being conducted to see if these medications could also act preventively against neurodegenerative diseases such as Alzheimer’s. But the study situation is not yet conclusive here.”
Also interesting: Charité Professor Andreas Michalsen: “Fasting for 7 to 10 Days Reduces Liver Fat by Half”
»So Far, No Evidence That GLP-1 Therapies Reduce Cancer Risk
What is the status of the much-discussed question of potential protection against cancer?
“In randomized, controlled trials–the highest class of evidence–there has been no indication so far that GLP-1 medications reduce cancer risk. But equally important: There is also no increased risk from GLP-1 therapies. This is, in my view, a very reassuring finding, especially given earlier discussions about pancreatic cancer.”
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Who Benefits Most from GLP-1 Medications
Who benefits the most from these medications–and are there also patient groups where the effect is limited?
“The strongest effect is seen in overweight patients with type 2 diabetes, especially if they already suffer from cardiovascular diseases or are on the verge of insulin therapy. But there are also so-called non-responders.”
»In 15 to 20 Percent of Patients, GLP-1 Has No Effect
In non-responders, does the therapy not work at all?
“Non-responders are people for whom neither significant weight loss nor good blood sugar control is achieved. They make up an estimated 15 to 20 percent. We see this particularly often in patients whose insulin production is already severely limited.”
In part 2 of the interview, metabolism specialist Norbert Stefan explains the adverse effects of GLP-1-based therapies. These range from frequent nausea to rare but serious risks or rare disorders.