GLP-1 diet: what to eat on weight loss medication

The 2024 Australian product information for semaglutide 2.4 mg reports that after 20 weeks of dosing, energy intake at a test meal where participants ate as much as they wanted was 35% lower than with placebo.¹

A 2025 joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society reports that medicines in this class reduce energy intake by 16% to 39% compared with placebo. It states that a reduction of this size can lead to insufficient intake of vitamins and minerals.²

The advisory lists regular, small meals at consistent times among eating habits to encourage, and long periods without meals among those to minimise. The advisory is an expert group's appraisal of published literature and clinical experience, not a trial of these habits. The two Australian consumer medicine information leaflets reviewed, one for semaglutide and one for tirzepatide, give no advice on meal size or meal timing.^{2, 3, 4}

healthdirect states: "It is important to eat enough food and nutrients each day." It says to speak to a doctor or dietitian to make sure nutrient needs are met. It also states that reduced appetite can mean no longer enjoying eating, and that for some people this may lead to an eating disorder.⁵

These are general population reference values. The joint advisory states that higher intakes of 1.2 to 1.6 g/kg per day have been proposed during active weight reduction. It states the basis (actual weight, adjusted weight or fat-free mass) is unclear.^{6, 2}

No trial in the sources reviewed tested a protein target in people using these medicines. An individual target is a question for a dietitian or doctor.²

• STEP 1 substudy (68 weeks, n=95 on semaglutide 2.4 mg, trial funded by Novo Nordisk): lean body mass fell 9.7%. The joint advisory reports 38% of weight lost in STEP 1 as lean body mass.^{7, 8, 2}
• SURMOUNT-1 substudy (72 weeks, n=124 on tirzepatide, authors include Eli Lilly employees): lean mass fell 10.9%, about 25% of weight lost.⁹
• Lean mass on a DXA scan includes muscle and other non-fat tissue.^{2, 7, 9}

The joint advisory states that increased protein intake alone "is likely inadequate" to preserve muscle without structured resistance training. It recommends strength training at least three times weekly. The National Heart Foundation of Australia's 2026 consensus statement recommends two days per week or more.^{2, 10}

These are general population reference values. The fibre figure is derived from median population intakes.¹¹

In placebo-controlled trials in the 2024 product information, constipation was reported by 21.8% of people taking semaglutide 2.4 mg and 10.2% taking placebo. In the tirzepatide weight management studies it was reported by 13.6% across doses and 5.2% taking placebo.^{1, 13}

The semaglutide consumer medicine information states that nausea, vomiting and diarrhoea "can cause dehydration (loss of fluids)" and that "it is important that you drink enough fluids to prevent dehydration", especially for people with kidney problems. The tirzepatide leaflet lists symptoms of dehydration: dry mouth, less frequent urination, dark urine, headache, muscle weakness or dizziness. Neither leaflet states a volume.^{3, 4}

The joint advisory says adequate fluids and fibre from foods should be encouraged for constipation, "although additional strategies are often required". No source reviewed shows that fibre prevents or treats constipation in people using these medicines.²

The Australian Dietary Guidelines (2013) use five food groups: vegetables; fruit; grain (cereal) foods; lean meat and poultry, fish, eggs, nuts and seeds, and legumes or beans; and milk, yoghurt, cheese or alternatives. One standard serve from the grain, meat and alternatives, or milk and alternatives groups provides about 500 to 600 kJ.^{14, 15}

The joint advisory states that insufficient vitamin and mineral intake is a particular risk at energy intakes below 1,200 kcal per day for females and 1,800 kcal per day for males. Converted by us at 4.184 kJ per kcal, that is about 5,000 kJ and 7,500 kJ. These are thresholds the advisory reports, not intake targets. The nutrients of concern it names include iron, calcium, magnesium, zinc and vitamins A, D, E, K, B1, B12 and C.²

On supplements, the advisory states that they "can be proactively considered for at-risk nutrients, such as vitamin D, calcium, B12, or a multivitamin-mineral tablet, at appropriate doses and tailored to each person's needs". A 2024 review funded by Eli Lilly, the manufacturer of tirzepatide, lists supplementation with vitamin D, calcium and a complete multivitamin as something for clinicians to consider. Neither source recommends supplements for everyone using these medicines.^{2, 16}

healthdirect says to speak to a doctor or dietitian to make sure nutrient needs are met each day.⁵

The two tables come from different trials and are not a comparison between medicines. Both documents describe most events as mild to moderate and more frequent during dose escalation. Gastrointestinal events led 4.3% of people taking semaglutide 2.4 mg to stop treatment permanently.^{1, 13}

The joint advisory says smaller, more frequent meals and avoiding fatty or high-fibre foods in the first few days of treatment "can help alleviate symptoms" of nausea, and that vomiting is more likely with large meals. For the first statement it cites clinical practice recommendations, not a trial. No source reviewed reports a trial showing that a food, drink or eating pattern prevents or treats these side effects. The two consumer medicine information leaflets reviewed give no advice on meal size or foods to avoid.^{2, 3, 4}

The semaglutide leaflet says: "Speak to your doctor if you have any of these less serious side effects and they worry you."³

The semaglutide consumer medicine information says: "Call your doctor straight away, or go straight to the Accident and Emergency Department at your nearest hospital if you notice any of these serious side effects." The tirzepatide leaflet gives the same instruction. The serious side effects listed are:^{3, 4}

• Severe stomach pain that is long-lasting or does not go away, which may be felt in the back, with or without vomiting (signs of an inflamed pancreas).^{3, 4}
• Breathing or swallowing problems, swelling of the face, mouth or throat, wheezing, rash or hives, fast heartbeat, or feeling dizzy or weak (signs of an allergic reaction).^{3, 4}
• Severe constipation with stomach ache, bloating or vomiting (bowel obstruction, semaglutide leaflet).³
• Sudden, severe pain in the upper stomach, fever, yellowing of the skin or eyes, or clay-coloured stools (gallbladder complaints, tirzepatide leaflet).⁴
• Changes to vision or loss of vision.^{3, 4}

The tirzepatide leaflet says to tell your doctor as soon as possible about severe abdominal pain, bloating, difficulty passing wind, or constipation or bowel urges with no resulting movement.⁴

Both leaflets warn of low blood sugar in people who also take a sulfonylurea or insulin. In June 2025 the Therapeutic Goods Administration announced a class-wide warning about inhaling stomach contents during general anaesthesia or deep sedation. The semaglutide leaflet says to tell your healthcare professional before such a procedure.^{3, 4, 17}

Accredited Practising Dietitian (APD) is the credential awarded under the national credentialing program run by Dietitians Australia. Dietitians Australia states that APDs are the only dietetic professionals recognised by Australian Government organisations, that APDs must log 30 hours of continuing professional development each year, and that nutritionists as a profession are not regulated.¹⁸

Under Medicare, a person with a GP chronic condition management plan may be eligible for up to 5 individual allied health services per calendar year, or up to 10 for Aboriginal or Torres Strait Islander patients. The services can be used with one profession or spread across several, including dietitians. A GP or prescribed medical practitioner must refer the patient. People with type 2 diabetes may also be eligible for one assessment and up to 8 group sessions per calendar year.^{19, 20}

Services Australia lists three Medicare items for individual dietitian services under these plans: 10954 (face to face), 93000 (video) and 93013 (phone). It states the health professional must treat the patient for at least 20 minutes.²⁰

The National Heart Foundation of Australia's 2026 consensus statement advises clinicians to consider referral to an APD for individualised nutrition care for people prescribed these medicines.¹⁰

• STEP 1 extension (semaglutide 2.4 mg, n=327 across semaglutide and placebo groups, exploratory analyses, STEP 1 funded by Novo Nordisk): mean weight loss with semaglutide was 17.3% at week 68. One year after the medicine and the lifestyle intervention were both withdrawn, these participants had regained 11.6 percentage points, a net loss of 5.6% at week 120. The authors describe this as regaining two-thirds of the prior weight loss.^{21, 8}
• STEP 4 (semaglutide 2.4 mg, 803 people randomised after a 20-week run-in, authors include a Novo Nordisk employee): from week 20 to week 68, mean body weight fell 7.9% with continued semaglutide and rose 6.9% after a switch to placebo. Both groups received a lifestyle intervention.²²
• SURMOUNT-4 (tirzepatide, 670 people randomised after a 36-week lead-in, sponsored by Eli Lilly): from week 36 to week 88, mean body weight fell 5.5% with continued tirzepatide and rose 14.0% after a switch to placebo.²³

These are trial averages and do not predict an individual result. None of these trials tested whether an eating pattern or a protein intake changes weight regain.^{21, 22, 23}

healthdirect states: "Weight loss medicines do not cure obesity. After you stop taking the medicine, it is important to maintain new habits around eating, exercise and lifestyle." Both consumer medicine information leaflets say not to stop the medicine without talking to your doctor.^{5, 3, 4}