Hunger is often discussed as a matter of willpower. In appetite research, it looks very different. Physiologists who study eating behaviour and metabolism see hunger as a fluctuating biological signal shaped by hormones, digestion, activity and environment. The recent surge of interest in GLP-1 drugs has brought one part of this system into public view.
GLP-1, or glucagon-like peptide-1, is a hormone produced naturally in the gut and plays a key role in controlling blood sugar, appetite and digestion. After eating, it helps signal fullness and slows the rate at which food leaves the stomach, shaping how quickly nutrients enter the bloodstream and how much energy the body takes in.
Appetite regulation begins in the gut rather than the brain alone. Signals from digestion, microbes and nutrient absorption activate hormonal pathways that travel to the brain through the bloodstream and nervous system.
Hunger is shaped by several of these signals. Ghrelin, released from the stomach, stimulates appetite. After food is eaten, levels of GLP-1 typically rise, helping signal satiety. Research shows appetite is closely linked to this increase in GLP-1 and how it communicates with brain regions involved in regulating eating.
Drugs such as Ozempic, Wegovy and Mounjaro are known as GLP-1 receptor agonists. They were originally developed for diabetes treatment and have been used to treat Type 2 diabetes since 2005. More recently, they have been prescribed for obesity management.
These medications activate the same biological pathways as natural GLP-1, but for much longer. Under normal conditions, GLP-1 rises for a relatively short period after eating, typically around two hours. This post-meal phase is when appetite is naturally suppressed and digestion slows. GLP-1 medications extend that state. Rather than simply blocking hunger, they maintain a physiological signal associated with having recently eaten.
This helps explain their impact. By reducing appetite and slowing gastric emptying, they can support sustained weight loss. But they also highlight how dynamic appetite is.
Research in exercise and nutrition shows that hunger does not increase in a simple, linear way with energy expenditure. Intense physical activity can temporarily suppress appetite through shifts in gut hormones, including GLP-1, even as energy needs rise.
Appetite often returns later as the body re-balances. In some cases, particularly after sessions such as high intensity intermittent training (HIIT), cravings for food can increase substantially.
Typically, weight loss of up to 5 to 8% can be achieved with a GLP-1 receptor agonist, although outcomes vary and tend to occur gradually over months. Medical advice should always be sought before starting treatment, and nutritional strategies should be discussed with a dietician or qualified nutritionist.
The rise of these medications has also reshaped how obesity is understood. For decades, weight was often framed primarily in terms of personal responsibility. GLP-1 therapies instead highlight the biological regulation of appetite and metabolism. They shift attention toward physiology and the gut-brain axis, rather than willpower alone, and have influenced public conversations about stigma, treatment access and the medicalisation of weight management.
Yet appetite reduction does not remove the body’s need for nutrients and fluids. When food intake falls, the challenge becomes maintaining nutritional balance. Hydration remains essential, as the body can lose around 2 to 3 litres of fluid each day through urine, sweat, breathing and bowel movements. Replacing this fluid supports circulation, temperature regulation and organ function. Hydration therefore remains fundamental even when appetite is reduced.
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Electrolytes also play a central role in nerve activity, muscle contraction and fluid balance. These charged minerals, including sodium, potassium, chloride, magnesium and calcium, are present in everyday foods and drinks, but reduced intake can lower overall levels.
Maintaining muscle mass is another consideration. When calorie intake drops substantially, the body may begin to break down muscle tissue for energy. Preserving muscle supports metabolic health and physical function. Protein intake of around 1.2 g per kg of body weight per day is often recommended, with sources including eggs, dairy, legumes, tofu and lean meats.
Changes in eating patterns can also affect digestion. Reduced food intake increases the likelihood of constipation, particularly if fibre consumption falls. Foods that are high in fibre help maintain bowel health by supporting regular movement and gut function.
Like most medications, GLP-1 drugs can have side effects. These may include nausea, abdominal discomfort, fatigue, bloating, constipation or diarrhoea. In some cases, there may be muscle loss and gallbladder problems. Ongoing monitoring is therefore important.
Another key question is what happens when treatment stops. Research suggests weight regain is common once medication is discontinued. When the prolonged satiety signal is removed, appetite-regulating hormones return to previous patterns. The biological drive to regain lost weight can re-emerge, highlighting that these drugs modify appetite while they are taken but do not permanently reset the systems that regulate it.
The wider implications extend beyond individual treatment. Appetite is influenced by multiple factors, including gut hormones, microbiome activity, physical activity, circadian rhythms and metabolic health. GLP-1 therapies interact with this wider system rather than replacing it. They also raise questions about long-term use, access and how food environments might respond to widespread appetite suppression.
From a physiological perspective, the significance of GLP-1 medications lies not only in their clinical effects but in what they reveal. Hunger is not a fixed trait. It is a fluctuating signal shaped by gut-derived hormones, digestion, activity and environment. These drugs amplify one part of that system by extending the post-meal state, but they do not replace the broader mechanisms that govern appetite, nutrition and metabolism.
Weight management therefore remains embedded in a wider biological and social context. Hormones matter, but so do daily routines, physical activity, food availability and long-term health patterns. GLP-1 therapies highlight how strongly biology shapes hunger, while also underscoring how complex and interconnected appetite regulation really is.
Lewis Mattin is affiliated with The Physiological Society, The Society for Endocrinology, UKRI funded Ageing and Nutrient Sensing Network, BBSRC UK GIBA network & SENr-Academic Associate Registration
