GLP-1 receptor agonists activate receptors involved in appetite and blood glucose regulation. They can reduce hunger and food intake, but their effects are not simply a matter of keeping food in the stomach longer. 1

Semaglutide targets GLP-1 receptors. Tirzepatide targets both GLP-1 and GIP receptors, making it a dual agonist rather than another version of the same medicine. 1 2

The incretin effect

The incretin effect describes a stronger insulin response to glucose taken by mouth than to glucose given intravenously, even when blood glucose levels are matched. Signals from the gut help explain the difference. 3

A small human study demonstrated a reduced incretin effect in type 2 diabetes. That does not establish that everyone with obesity has a faulty appetite system: insulin secretion and hunger are different outcomes. 3

Semaglutide activates the receptor used by natural GLP-1. Resistance to DPP-4 breakdown and binding to albumin, a blood protein, prolong its action and allow weekly dosing. 1

For differences between medicines, see our semaglutide, tirzepatide and retatrutide comparison.

Gastric emptying and appetite regulation

GLP-1 signalling influences appetite through the brain. Animal studies identify pathways involving the hypothalamus and brainstem; human studies show reduced hunger and cravings. These are related but different kinds of evidence. 1

Gastric emptying means movement of food from the stomach into the small intestine. Tirzepatide slows this process most after the first dose, with the effect diminishing over time. 2

In a 20-week trial involving 72 adults with obesity, semaglutide reduced appetite and food intake without a detectable delay in gastric emptying at the final assessment. 4

However, researchers used paracetamol absorption as an indirect test. This does not prove that gastric emptying is unaffected in every person or under every treatment condition. 4

The practical distinction is important: appetite suppression can persist without a consistently large stomach-emptying delay. Feeling fuller does not tell you exactly how quickly your stomach is emptying. 4

Glucose metabolism

These medicines increase insulin secretion when glucose is elevated and reduce glucagon, which helps limit glucose release from the liver. Glucose dependence means insulin stimulation decreases as glucose falls. 1 2

This does not make hypoglycaemia impossible. Risk increases with insulin or sulfonylureas, so your prescriber should review the combination. Do not adjust medication yourself. 2

Insulin sensitivity can also improve during treatment. Tirzepatide studies demonstrate this, but weight reduction may contribute. It should not be presented as a universal, independent fat-burning mechanism. 2

Nor does improved glucose control guarantee muscle preservation. Semaglutide body-composition data show reductions in both fat and lean mass, with more fat lost. 1

Why nutrition strategy matters

Eating less can make protein, vitamin and mineral needs harder to meet, but deficiency is not inevitable. A useful plan supports adequate intake rather than pushing appetite suppression further. 5

Start with these practical steps:

  • Include protein in meals, such as eggs, fish, yoghurt, tofu or beans. 5
  • Use smaller meals if large portions are uncomfortable, while retaining fruit, vegetables and other nutrient-rich foods. 5
  • Drink regularly and discuss persistent poor intake with your care team. 5
  • Pair adequate protein with suitable resistance training. Protein alone cannot guarantee muscle preservation. 5

These priorities reflect professional guidance, not proof that one meal plan is best. Individual needs and tolerances differ. 5

Our GLP-1 nutrition strategy guide covers planning in more detail. Optional nutrition coaching can support the practical work alongside your medical care.

The NZ regulatory context

As checked on 6 September 2026, Wegovy has NZ approval for chronic weight management. Mounjaro has approval for type 2 diabetes and chronic weight management, subject to their labelled criteria. 1 2

Neither product is Pharmac-funded. Approval and funding are separate, and neither guarantees stock at a particular pharmacy. Ask your pharmacy about supply and private cost. 6

Dulaglutide and liraglutide are funded for eligible people with type 2 diabetes under Special Authority. Expanded criteria took effect on 1 September 2026; this is not general weight-loss funding. 7

See GLP-1 access in New Zealand for the access-focused guide.

The role of body composition monitoring

Scale weight cannot separate fat from other body components. BIA estimates fat and fat-free mass using electrical measurements and prediction equations; it does not directly identify tissue lost each week. 8

Lean mass is not synonymous with skeletal muscle. A reported reduction cannot automatically be labelled muscle loss. 5

Hydration, recent meals and exercise can change BIA results. If scans are used, keep measurement conditions consistent and interpret trends cautiously rather than reacting to one weekly reading. 8

For measurement choices and limitations, read BIA versus DEXA.

Treatment duration and when to seek help

These medicines are used for chronic weight management, not only as short-term appetite tools. Duration should be reviewed with your prescriber rather than determined by a coaching programme. 1 2

Seek urgent medical advice for severe, persistent abdominal pain, especially with vomiting. Persistent vomiting or inability to keep fluids down also needs prompt assessment because dehydration can affect kidney function. 2

Tell your anaesthesia or procedure team that you take the medicine before planned sedation or surgery. Medication decisions, including any interruption, belong with the treating team. 2