Saxenda (liraglutide 3.0 mg) is a prescription GLP-1 receptor agonist licensed in the UK for weight management in adults with obesity or overweight with comorbidities. Intermittent fasting is a dietary pattern alternating between eating and fasting periods. Whilst both approaches aim to support weight loss, there is no official UK guidance on combining Saxenda and intermittent fasting. The clinical trials supporting Saxenda's approval did not investigate this combination, meaning evidence on safety and efficacy remains limited. This article examines the pharmacology of both approaches, potential benefits and risks of combining them, and NHS recommendations for safe weight management.

What Is Saxenda and How Does It Work?

Saxenda (liraglutide 3.0 mg) is a prescription-only medicine licensed in the UK for weight management in adults with obesity (BMI ≥30 kg/m²) or those who are overweight (BMI ≥27 kg/m²) with at least one weight-related comorbidity, such as type 2 diabetes, hypertension, or dyslipidaemia. It is also licensed for weight management in adolescents aged 12-17 years with body weight above 60 kg and obesity. Saxenda is manufactured by Novo Nordisk and approved by the Medicines and Healthcare products Regulatory Agency (MHRA).

Saxenda belongs to a class of medications known as glucagon-like peptide-1 (GLP-1) receptor agonists. Liraglutide mimics the action of the naturally occurring hormone GLP-1, which is released from the intestine after eating. The drug works through several mechanisms to support weight loss: it slows gastric emptying (meaning food stays in the stomach longer), reduces appetite by acting on areas of the brain that regulate hunger, and promotes a feeling of fullness or satiety after meals. These combined effects help patients consume fewer calories without experiencing intense hunger.

Saxenda is administered as a once-daily subcutaneous injection, typically in the abdomen, thigh, or upper arm. The dose is gradually increased over five weeks, starting at 0.6 mg daily and building up to the maintenance dose of 3.0 mg daily, which helps minimise gastrointestinal side effects. According to the UK product licence (SmPC) and BNF, Saxenda should only be continued in adults if patients achieve at least 5% weight loss after 12 weeks of treatment at the full dose, or in adolescents if there is a reduction of at least 4% in BMI standard deviation score after 12 weeks at the maximum tolerated dose.

Saxenda should not be used during pregnancy or breastfeeding, or in combination with other GLP-1 receptor agonists. Important safety considerations include risks of pancreatitis, gallbladder disease, increased heart rate, and potential mood changes. It is intended to be used alongside a reduced-calorie diet and increased physical activity, not as a standalone treatment.

Understanding Intermittent Fasting for Weight Loss

Intermittent fasting (IF) is a dietary pattern that cycles between periods of eating and voluntary fasting on a regular schedule. Unlike traditional calorie-restricted diets that focus on what you eat, intermittent fasting primarily concerns when you eat. Several popular approaches exist, including the 16:8 method (fasting for 16 hours and eating within an 8-hour window), the 5:2 diet (eating normally for five days and restricting calories to around 500–600 on two non-consecutive days), and alternate-day fasting.

The primary mechanism behind intermittent fasting's effects on weight loss is creating a calorie deficit by limiting the time available to consume food. There is also emerging, though mixed, evidence suggesting it may improve insulin sensitivity, promote fat oxidation, and potentially trigger metabolic switching from glucose-based to ketone-based energy. Some research suggests that IF may influence hormones related to hunger and satiety, such as ghrelin and leptin, though evidence remains limited.

Weight loss outcomes from intermittent fasting vary considerably between individuals. Systematic reviews indicate that IF can produce similar weight loss to continuous calorie restriction when overall energy intake is comparable. However, adherence can be challenging, and intermittent fasting is not suitable for everyone. Certain groups should avoid IF, including pregnant or breastfeeding women, children and adolescents, individuals with a history of eating disorders, and those with certain medical conditions such as type 1 diabetes. People taking insulin or sulfonylureas need individualised medical advice due to hypoglycaemia risk.

It is important to note that whilst intermittent fasting has gained popularity, long-term safety and efficacy data remain limited. The NHS advises that any significant dietary change should be discussed with a healthcare professional, particularly for individuals with existing health conditions or those taking medications that could be affected by altered eating patterns.

Can You Combine Saxenda with Intermittent Fasting?

There is no official guidance from NICE, the MHRA, or the manufacturer specifically addressing the combination of Saxenda with intermittent fasting. The clinical trials that led to Saxenda's approval did not investigate this particular combination, meaning there is limited evidence regarding safety, efficacy, or potential interactions when these two approaches are used together. Any benefits or risks of combining these approaches remain theoretical.

From a pharmacological perspective, combining Saxenda with intermittent fasting presents several considerations. Saxenda works by slowing gastric emptying and reducing appetite throughout the day, effects that persist regardless of eating schedule. Intermittent fasting, meanwhile, restricts the time window during which food is consumed. Theoretically, both approaches aim to reduce overall calorie intake, which could lead to an additive effect on weight loss. However, this combination might also increase the risk of certain adverse effects.

Gastrointestinal side effects are among the most common with Saxenda, including nausea, vomiting, diarrhoea, and constipation. These effects are often most pronounced when starting treatment or increasing the dose. Combining Saxenda with intermittent fasting—particularly more restrictive fasting protocols—could potentially exacerbate these symptoms or make them more difficult to manage. It's worth noting that Saxenda can be taken at any time of day, with or without food, and timing can be adjusted for tolerability.

Another important consideration is hypoglycaemia risk. While liraglutide alone has a low risk of causing hypoglycaemia, this risk increases in patients with type 2 diabetes who are taking insulin or sulfonylureas alongside Saxenda. For these individuals, fasting periods could increase the risk of low blood sugar. Patients should not alter their eating patterns significantly without first consulting their prescribing clinician, who can assess individual risk factors and adjust medications if necessary. Any decision to combine these approaches should be made collaboratively with a healthcare professional who can provide personalised advice based on medical history and current health status.

Potential Benefits and Risks of Using Both Together

The potential benefits of combining Saxenda with intermittent fasting are largely theoretical, as no robust clinical trials have specifically examined this combination. Some individuals might experience enhanced weight loss due to the complementary mechanisms: Saxenda reduces appetite and promotes satiety, whilst intermittent fasting restricts eating windows and may create a larger calorie deficit. For patients who find intermittent fasting sustainable, the appetite-suppressing effects of Saxenda might make fasting periods more tolerable and reduce the likelihood of overeating during eating windows.

However, several significant risks and concerns must be considered:

• Excessive calorie restriction: Combining two weight loss methods could result in inadequate nutritional intake, potentially leading to nutrient deficiencies, muscle loss, fatigue, and other health complications. Severe calorie restriction is not recommended and can be counterproductive to long-term weight management.

• Increased gastrointestinal side effects: Nausea, vomiting, and other digestive symptoms associated with Saxenda may be worsened when fasting, potentially affecting treatment adherence and quality of life.

• Hypoglycaemia risk: Particularly concerning for patients taking insulin or sulfonylureas alongside Saxenda, the combination of reduced food intake and glucose-lowering medications could lead to dangerously low blood sugar levels, which require immediate medical attention.

• Dehydration and kidney problems: Both Saxenda (through gastrointestinal effects) and fasting can increase dehydration risk, which may impact kidney function. Adequate fluid intake is essential, but this can be challenging if nausea is present.

• Pancreatitis and gallbladder disease: Saxenda carries risks of pancreatitis and gallbladder problems, which could potentially be exacerbated by rapid weight loss and dehydration.

• Mood changes: Saxenda may affect mood in some people, and combining with fasting could potentially influence this further.

• Sustainability concerns: Combining two restrictive approaches may be difficult to maintain long-term, potentially leading to weight regain once either or both interventions are discontinued.

Patient safety advice: If you are taking Saxenda and considering intermittent fasting, you should contact your GP or prescribing clinician before making any changes to your eating pattern. Warning signs that require immediate medical attention include severe or persistent abdominal pain (especially if radiating to the back), severe or persistent nausea and vomiting, signs of dehydration (dark urine, dizziness, reduced urination), symptoms of hypoglycaemia (shakiness, confusion, sweating, rapid heartbeat), jaundice or right upper quadrant pain, or mood changes including depression or suicidal thoughts. Regular monitoring and open communication with healthcare providers are essential for safe weight management. Suspected side effects should be reported via the MHRA Yellow Card Scheme.

NHS Guidance on Safe Weight Management Approaches

The NHS recommends a gradual, sustainable approach to weight loss, typically aiming for 0.5 to 1 kg (1 to 2 lbs) per week. This is best achieved through a combination of a balanced, reduced-calorie diet and increased physical activity. NICE guidance emphasises that weight management interventions should be multicomponent, addressing dietary intake, physical activity levels, and behaviour change strategies.

For individuals with obesity, NICE Clinical Guideline CG189 and Public Health Guideline PH53 outline a tiered approach to weight management. Initial interventions focus on lifestyle modifications, including dietary changes and physical activity. Pharmacological treatments like Saxenda are reserved for those who have not achieved adequate weight loss through lifestyle changes alone and who meet specific BMI and comorbidity criteria. Importantly, NICE stipulates that weight-loss medications should always be used as part of a comprehensive weight management programme, not in isolation. Access to pharmacotherapy on the NHS is subject to local commissioning arrangements and NICE technology appraisals.

Regarding intermittent fasting specifically, the NHS acknowledges it as one of several dietary approaches that some people find helpful for weight loss. However, the NHS emphasises that there is no single "best" diet for everyone, and the most effective approach is one that an individual can maintain long-term. The NHS website advises that people considering intermittent fasting should ensure they still consume adequate nutrients and maintain a balanced diet during eating periods.

Key NHS recommendations for safe weight management include:

• Consulting a GP before starting any weight loss programme, particularly if you have existing health conditions or take regular medications

• Focusing on sustainable lifestyle changes rather than quick fixes or extreme restrictions

• Ensuring adequate intake of essential nutrients, including protein, vitamins, and minerals

• Incorporating regular physical activity (at least 150 minutes of moderate-intensity or 75 minutes of vigorous activity per week, plus muscle-strengthening activities on at least 2 days per week)

• Seeking support from healthcare professionals, registered dietitians, or structured weight management programmes

• Monitoring for any adverse effects and reporting concerns promptly to your healthcare provider

For patients prescribed Saxenda, adherence to the prescribing clinician's instructions is essential, including attending regular follow-up appointments to monitor progress, assess tolerability, and determine whether continued treatment is appropriate. Weight management is a long-term commitment, and the most successful approaches are those that can be integrated into daily life sustainably whilst supporting overall health and wellbeing.

Frequently Asked Questions