Why protein matters during weight loss

Most people have no idea how important muscle is until they start losing it. Unfortunately, this can happen during weight loss if you do not eat enough protein or do not challenge your muscles with resistance exercise.

Whenever we lose weight, we usually lose a combination of body fat and lean tissue. The goal is not simply to make the number on the scales go down. The goal is to lose body fat while preserving as much muscle as possible.

Muscle is metabolically active tissue. It supports strength, movement, mobility, healthy ageing, blood sugar regulation and overall metabolic health. Losing too much muscle during weight loss can slow metabolism, reduce strength, impair mobility and make long-term weight maintenance more difficult.

This is particularly important during rapid weight loss, restrictive eating, or when appetite is significantly reduced. It is also highly relevant for people taking GLP-1 medications, because these medications often reduce appetite and overall food intake.

Using a body composition scale, rather than relying on body weight alone, can help you monitor changes in muscle mass throughout your journey. Body composition scales are not perfect, but they can help you notice trends over time. Two people may lose the same amount of weight, but one may lose mostly fat while the other may lose more lean tissue.

Why protein matters during weight loss

Protein is important at every stage of weight loss and, in reality, throughout life. While it plays a key role in protecting muscle during calorie restriction, its benefits extend far beyond muscle alone.

Protein helps preserve muscle mass

Whenever we lose weight, we lose both fat and muscle. Higher-protein diets help reduce muscle loss during periods of calorie restriction (Ref. 2). This is particularly important when appetite is low, or weight loss is happening quickly.

Protein helps you feel fuller for longer

Protein stimulates the release of hormones such as CCK, PYY and GLP-1, which increase satiety and reduce hunger (Ref. 3). This can make it easier to manage appetite, reduce grazing and support long-term weight maintenance.

Protein supports weight loss and maintenance

Research shows that higher-protein diets can improve weight loss and reduce the likelihood of weight regain (Ref. 4). Protein can make a healthy, calorie-controlled approach easier to sustain.

Protein supports metabolism

Protein has a higher thermic effect than carbohydrate or fat, meaning your body uses more energy to digest and process it, slightly increasing daily energy expenditure (Ref. 5). The effect is modest, but every supportive strategy matters during weight loss.

Protein helps maintain strength and healthy ageing

Muscle is one of the body’s largest metabolic organs. Eating enough high-quality protein, together with resistance exercise, supports muscle repair, strength, mobility and independence (Ref. 6). This is particularly important from midlife onwards.

Protein supports bone health

Bone is made from a protein matrix as well as minerals such as calcium and phosphorus. Adequate protein intake contributes to bone maintenance alongside sufficient calcium, vitamin D and regular weight-bearing exercise (Ref. 7).

Protein supports healthy hair

Hair is made primarily from keratin, a structural protein. During periods of rapid weight loss or restrictive eating, inadequate protein intake may contribute to increased shedding and slower hair growth, although many other factors can also play a role (Ref. 8, 9).

Protein is essential for hormones, enzymes and immune function

Amino acids are required to produce hormones, digestive enzymes, antibodies and many other compounds essential for normal health (Ref. 10 and 11). Protein is therefore not only about muscles. It is involved in repair, recovery and general well-being.

Protein and GLP-1 medications

Protein is important for anyone losing weight, but it becomes even more important when taking GLP-1 medications.

Muscle loss is often blamed on GLP-1 medications. You may have heard of “Ozempic face” or read that up to 40% of weight lost during GLP-1 treatment may come from lean tissue (Ref. 1). However, the medication itself is not directly damaging your muscles. Any rapid weight loss, regardless of how it is achieved, can result in the loss of both fat and muscle.

Preserving muscle becomes a priority when taking GLP-1 medication because appetite is reduced and food intake naturally falls. This can be very helpful for weight loss, but it can also make it harder to meet your protein and micronutrient needs.

If you are eating much smaller portions, skipping meals, or feeling full very quickly, protein can easily fall too low. Over time, this may increase the risk of muscle loss, fatigue, weakness, hair shedding and poorer nutritional status.

This does not mean GLP-1 medications are bad for muscle. It means they need to be used alongside a sensible nutrition and lifestyle plan. The aim is to support fat loss while protecting strength, muscle and long-term metabolic health.

How much protein do you need?

Current UK recommendations for healthy adults are approximately 0.75 g of protein per kilogram of body weight per day (Ref. 12). For someone weighing 60 kg, this equates to approximately 45 g per day.

However, these recommendations are designed to prevent deficiency rather than optimise health. They are not necessarily the best target for someone who is actively losing weight, taking medication that reduces appetite, exercising, or trying to protect muscle mass.

Research suggests that physically active adults, older adults and people trying to preserve muscle during weight loss often benefit from higher intakes, typically between 1.2 and 2.0 g/kg/day (Ref. 13).

Specific guidance for people taking GLP-1 medications is still emerging. Recent reviews suggest aiming for 60-75 g daily, with intakes up to 1.5 g/kg body weight during weight reduction (Ref. 14).

In my own practice, I have found that many people taking GLP-1 medications require around 100 g of protein per day to help preserve muscle mass during weight loss. This is not an official recommendation, but it reflects my experience working with clients, especially those whose appetite drops significantly.

Rather than focusing on one large serving, aim to spread protein across the day. As a guide, include 20 to 30 g of protein per meal, along with one or two protein-rich snacks as needed. This is often easier than trying to eat one very large portion at dinner, especially if nausea, early fullness or reflux are present.

Examples of protein-rich snacks:

• Greek yoghurt with berries
• cottage cheese
• eggs
• chicken or turkey slices
• salmon or mackerel with sourdough
• peanut or almond butter with apple
• protein shakes when appetite is low
• a high-protein smoothie with approximately 40 to 50 g of protein

To make a higher-protein smoothie, blend milk or a fortified milk alternative with Greek yoghurt, protein powder, fruit such as berries, apple or banana, greens such as spinach or kale, one tablespoon of nut butter and one tablespoon of chia or flaxseeds.

Smoothies can be particularly useful at breakfast, after exercise, or during periods when solid food feels less appealing.

Does the type of protein matter?

Yes. Not all proteins provide the same amino acid profile. To effectively maintain or build muscle, the body needs all nine essential amino acids, which must come from food because it cannot make them.

Complete protein sources include:

• meat
• fish
• poultry
• eggs
• dairy products
• whey protein
• soy foods such as tofu, tempeh and edamame

Animal proteins are usually complete proteins, meaning they provide all nine essential amino acids in useful amounts. Some plant proteins, such as soy, are also complete. Other plant proteins may be lower in one or more essential amino acids, but this does not mean they are poor choices.

People following vegetarian or vegan diets can absolutely meet their protein requirements, but it often requires a little more planning. Combining different plant protein sources throughout the day, such as beans with grains or hummus with wholemeal pitta, provides all the essential amino acids the body requires.

Plant-based clients may need larger portions or more frequent protein sources. Useful options include tofu, tempeh, edamame, lentils, chickpeas, beans, quinoa, soya yoghurt, pea protein, hemp seeds and mixed plant protein powders.

Practical strategies to increase protein

Meeting higher protein targets can feel challenging when your appetite is reduced. Fortunately, a few simple habits can make a big difference:

• aim for a source of protein at every meal, ideally around 20-30 g
• eat protein first before moving on to other foods
• spread protein evenly across the day rather than eating most of it in the evening
• include one or two protein-rich snacks if needed
• choose softer protein options, such as yoghurt, cottage cheese, eggs, fish, or smoothies, if heavier foods feel difficult to manage
• consider using a protein shake during periods when appetite is very low
• combine adequate protein intake with regular resistance exercise to protect muscle

Eating protein first is a simple but powerful strategy. When appetite is low, it is easy to fill up quickly on salad, soup, fruit or toast and then not manage the protein portion. Starting with protein helps make sure the most important nutrient is prioritised before you become too full.

Resistance exercise is equally important. Protein provides the building blocks, but your muscles also need a reason to stay. Strength training, Pilates, bodyweight exercises, resistance bands or weights can all help signal that muscle tissue is needed. Aim for an approach that is safe, realistic, progressive and appropriate for your fitness level.

There are hundreds of protein powders available, but choosing one does not need to be complicated.

Look for products with:

• around 20 to 30 g of protein per serving
• a short ingredient list
• minimal added sugar, especially if you are using it regularly
• a complete protein source such as whey protein isolate, or a blended plant protein if you follow a vegan diet
• a flavour and brand that you genuinely enjoy, making it easier to use consistently

Whey protein isolate is often well tolerated and provides a high-quality complete protein. Whey concentrate is also useful, although it contains slightly more lactose and carbohydrate. For people who avoid dairy, a pea and rice protein blend can work well.

Protein powders should supplement a balanced diet rather than replace whole foods. Whole foods provide additional nutrients such as iron, zinc, calcium, omega-3 fats, fibre and phytonutrients. However, protein powders can be extremely helpful during periods of reduced appetite.

The bottom line

Protein should be one of your highest nutritional priorities during weight loss, whether you are losing weight through lifestyle changes, calorie reduction, increased exercise, or GLP-1 medication.

Successful weight loss is about much more than seeing a lower number on the scales. The aim is to lose fat while preserving the muscle that keeps your metabolism healthy, supports movement and protects long-term health.

To help achieve this:

• include 20-30 g of protein at each meal and choose protein-rich snacks as needed
• eat your protein first, then move on to vegetables, carbohydrates, and fats
• use protein powders or ready-made shakes if reduced appetite makes eating enough difficult
• combine adequate protein intake with regular resistance training to maintain and build muscle
• monitor body composition where possible, not just body weight

With the right knowledge, planning and support, it is possible to lose fat while preserving muscle. Protein is not only important during GLP-1 treatment. It is one of the foundations of healthy, sustainable weight loss and good health for life.

Disclaimer: This article is for educational purposes only. I am not a medical doctor and do not prescribe weight loss medications. Always consult your GP, prescribing clinician or another appropriately qualified healthcare professional before making significant dietary changes or using supplements alongside GLP-1 medications, especially if you have an existing medical condition.

References

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