How Much Weight Should You Lose Per Week for Sustainable Weight Loss? (Including GLP-1 Medications)
- Amanda Duncan
- Jan 13
- 6 min read
It's January and after all the fun and indulgences of December, it feels like we've come down to earth with an almighty thud. At this time of year, many of us start thinking about a “reset” and for many people that includes weight loss goals. Whilst on this journey, who doesn’t feel the urge to shift the pounds as fast as possible and fit into that favourite pair of trousers again? The key thing to bear in mind though is that when it comes to long-term sustainability, faster isn’t always better.
This is especially relevant when considering the increasing use of GLP-1 medications such as Wegovy and Mounjaro (often referred to as weight-loss injections). A recent UCL study estimated that nearly 1 in 10 adults in Britain have either used a weight-loss medication or are considering doing so in the future (1). These medications work by reducing appetite and increasing feelings of fullness, which can lead to more rapid weight loss.
Whether weight loss is supported by medication or achieved without it, quick progress can feel motivating at first. However, losing weight too rapidly can come with downsides. This article explains what a sustainable rate of weight loss looks like, when weight loss may be happening too fast, and why this matters for both GLP-1 users and non-users alike.
What is a sustainable weight loss per week?
The NHS recommends aiming for 0.5–1 kg (1–2 lb) of weight loss per week for sustainable results (2). That said, weight loss rates vary between individuals and are influenced by factors such as starting weight, age, health conditions, stress levels, physical activity and medication use (3).
It’s also common to see faster weight loss during the first few weeks. This early drop is largely due to the body releasing stored water and glycogen (stored carbohydrate), rather than a large loss of body fat. True fat loss tends to be slower and often becomes more noticeable from around week three onwards.
When is weight loss potentially too fast?
Research shows that gradual weight loss (around 1–2 lb per week) leads to a greater proportion of fat loss. In contrast, faster weight loss increases the risk that more of the weight lost comes from lean tissue, including muscle, rather than fat. It may also trigger metabolic slowdown (4).
In practical terms, this means slower and steadier weight loss is more likely to reduce body fat whilst preserving muscle and keeping metabolism working efficiently. Losing muscle can make long-term weight maintenance harder as muscle plays a key role in maintaining metabolic rate, strength and weight stability.
This is particularly relevant for people using GLP-1 medications, as appetite suppression can make it easy to unintentionally undereat. However, similar risks can also occur with very low-calorie diets or overly restrictive approaches in people not using medication.
Why Rapid Weight Loss Can Increase Muscle Loss
A key risk of rapid weight loss is the loss of lean muscle mass. When calorie intake is too low, the body looks for alternative sources of energy. As a result, both fat and muscle tissue may be broken down to meet energy demands
Muscle is not just about strength or appearance. It plays an important role in:
Supporting metabolic rate
Maintaining strength and mobility
Protecting bone health (see my previous blog for future info on bone health)
Reducing the risk of weight regain
This is why adequate protein intake and resistance-based exercise are key to prevent muscle loss as part of any weight loss plan. This applies whether weight loss is driven by medication, dieting, or a combination of both.
The Impact of Fast Weight Loss on Metabolism and Hormones
Rapid weight loss can lead to metabolic adaptation, where the body responds to perceived under-fuelling by conserving energy. In practical terms, this means the body may enter a form of “survival mode,” burning fewer calories and increasing hunger signals. Over time, this can make weight loss feel harder and increase the risk of regaining weight once dieting becomes difficult to maintain.
Slower, steadier weight loss gives the body time to adjust without triggering these energy-saving responses. This helps support a healthier metabolism and makes long-term weight maintenance more achievable (4).
It’s important to note that whilst someone remains on GLP-1 medication, appetite-suppressing effects may mask some of these responses. However, metabolic adaptation can become more relevant when medication is reduced or stopped, making sustainable habits particularly important.
Why Slower Weight Loss Supports Long-Term Behaviour Change
Weight loss isn’t just about food. It also involves habits, routines, emotions and behaviours, all of which take time to develop and maintain.
Losing weight at a slower pace allows space to build consistent eating patterns, focus on nourishment rather than restriction, and develop coping strategies around emotional eating where relevant. It can also reduce all-or-nothing thinking, which is one of the biggest barriers to maintaining weight loss long term.
When weight loss happens very quickly, progress may rely heavily on appetite suppression or strict rules. In contrast, learning sustainable behavioural skills supports long-term success and allows life to remain enjoyable rather than overly restrictive!
GLP-1 Medications and the Speed of Weight Loss
GLP-1 medications can lead to faster weight loss by (5):
Reducing appetite
Increasing feelings of fullness
Slowing gastric emptying
Without a clear nutrition plan alongside medication use, there may be an increased risk of (6):
Skipping meals
Low protein and fibre intake
Micronutrient deficiencies
Side effects such as nausea or constipation
Without structured support, weight loss on GLP-1 medications can become too rapid, increasing the likelihood of muscle loss, fatigue, and weight regain once medication is adjusted or stopped. With appropriate nutritional guidance and professional support, these risks can be reduced. I have covered more strategies for managing side effects in my previous blog.
The Risk of Undernutrition with Rapid Weight Loss
One of the biggest risks when appetite is significantly reduced- whether through medication, restrictive dieting, or both- is undernutrition. Eating less overall can make it harder to meet requirements for key nutrients such as protein, fibre, iron, calcium, vitamin B12 and omega-3 fats.
Over time, inadequate intake can contribute to fatigue, muscle loss, hair loss, poor gut health, weakened immunity and reduced bone health. These risks are higher when meals are skipped, food variety is limited, or weight loss is very rapid. Regular meals and nutrient-dense food choices remain essential, even when portion sizes are smaller. For tips on what to eat whilst taking GLP-1 medications check out my blog post here.
What Sustainable Weight Loss Actually Looks Like
Sustainable weight loss is not defined solely by the number on the scales. It's also involves maintaining:
Stable energy levels
Preserved muscle strength
Whilst being mindful of:
Steady, manageable weight changes
Adequate protein and fibre intake
Regular meals and snacks
Habits that feel realistic and maintainable
To achieve weight loss goals, it's also not just about food. Laying sound foundations to health also covers key areas such sleep, stress support, exercise and hydration, as covered in my previous blog here.
How to Slow Weight Loss Safely If It’s Happening Too Fast
If weight loss feels uncomfortable or too rapid, supportive strategies which are worth trying and incorporating into your plan are:
Increasing protein intake with sufficient fibre
Eating regular, structured meals
Incorporating resistance /strength training
Supporting digestion and managing side effects
Reviewing overall energy intake with a professional
Slowing weight loss is not a failure. In many cases, it’s a sign of prioritising health and long-term success.
Final Thoughts
Although rapid weight loss may feel rewarding initially, slower, supported weight loss is often more sustainable and protective, particularly for people using GLP-1 medications. Focusing on nutrition, behaviour change, and long-term habits helps turn short-term results into lasting outcomes.
Nutrition and Behaviour Change Support
If you’re looking to lose weight and feel your weight loss is happening too quickly or without structure, professional nutrition and behaviour support can help protect both your health and results. If this is relevant to you and you'd benefit from some advice, please book in with me for a free 20 minute call here, I'd love to help.
About Amanda
Amanda is a London Nutritionist who supports clients online and in person with GLP-1 Nutrition Support and offers specific programmes: Optimising Health, Gut Health, Women's Health and Menopause. She also has a passion for all things Health and Corporate Wellbeing. Read more about Amanda here.
References:
Jackson, S. E., et al. (2026), 'Prevalence of use and interest in using glucagon like peptide-1 receptor agonists for weight loss: a population study in Great Britain', BMC Medicine.
NHS (2023), 'Tips to help you lose weight', Tips to help you lose weight - NHS
DeDent R, McPherson R, Harper ME, (2020), 'Factors affecting weight loss variability in obesity, Metabolism, Dec (119L154388).
Ashtary-Larky D, Bagheri, R, Abbasnezhad A et al. (2020), 'Effects of gradual weight loss v. rapid weight loss on body composition and RMT: a systematic review and meta-analysis, Br J Nutr, Dec (14, 124, 11), 1121-1132.
Moiz A, Filion KB, Tsoukas, MA et al. (2025), 'Mechanisms of GLP-1 Receptor Agonist-Induced Weight Loss: A Review of Central and Peripheral Pathways in Appetite and Energy Regulation,' Am K Med, June (138,6): 934-940.
Mozaffarian D, Agarwal M, Alexander L. et al, (2025), Nutritional Priorities to Support GLP-1 Therapy for Obesity: A Joint Advisory From the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and the Obesity Society, Am J Lifestyle Med, May(30), 1559876251344827.
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