Weight, Your Joints and Why Losing Weight Can Make Such a Difference
If you have painful knees, hips or other weight-bearing joints, you may have been told that losing weight could help. It is easy for this advice to sound overly simplistic: “Lose some weight and your joints will feel better.” But there is actually some fascinating science behind it.
Your joints don't simply experience the number you see on the bathroom scales. Every time you stand, walk, climb stairs or get up from a chair, forces are generated by your muscles and transmitted through your joints. The forces experienced by a knee during everyday movement can therefore be several times greater than your body weight.
This is particularly important for the knee because it is repeatedly loaded throughout the day.
Walking involves thousands of individual loading cycles. If you are carrying an additional 10 or 20 kg, that extra weight isn't just present once — it is being carried and mechanically dealt with every time you take a step.
The good news is that this also works in reverse. Losing weight can reduce the mechanical demand placed on your joints, and even relatively modest weight loss can be worthwhile.
How much force actually goes through your knee?
One of the most useful pieces of research for explaining the relationship between weight and knee loading comes from a study of people who were overweight or living with obesity and had knee osteoarthritis. Researchers used three-dimensional gait analysis to measure what happened to the forces through the knee when people lost weight.
They found that a reduction of approximately 1 kg in body weight was associated with a reduction of about 4 kg in the compressive force experienced by the knee during walking. The researchers also found reductions in other measures of knee loading. The important point is that the reduced force is repeated over and over again as we walk. (Messier et al., Arthritis & Rheumatism)
This gives us a useful way of visualising the potential effect:
Weight lost | Approximate reduction in knee force during walking* |
1 kg | 4 kg |
5 kg | 20 kg |
10 kg | 40 kg |
15 kg | 60 kg |
20 kg | 80 kg |
This is an approximate relationship from research in people with knee osteoarthritis. It should not be interpreted as saying that exactly 4 kg of force disappears from every person's knee during every activity.
The important point isn't necessarily the exact number. It is the principle: a relatively small reduction in body weight can produce a disproportionately larger reduction in the mechanical forces experienced by the knee during walking.
So if someone loses 10 kg, they have not simply removed a 10 kg weight from their body. The research suggests that this could translate into approximately 40 kg less knee compressive force during walking, on average. When that step is repeated thousands of times a day, the cumulative effect becomes much more significant.
Your knee doesn't experience the same load all the time
Different activities place very different demands on the knee. Walking, climbing stairs, getting up from a chair and running are not mechanically equivalent.
Recent research looking at knee loading and pain during everyday activities found that walking, stair climbing and sit-to-stand movements all produce different patterns of knee loading. Walking generated particularly high knee loads, while stair climbing was particularly demanding in terms of pain for people with knee osteoarthritis. (PubMed)
This helps explain why someone with knee arthritis may find that walking for ten minutes is difficult, stairs are particularly painful, but cycling or exercising in water is much more comfortable.
It also explains why reducing body weight can be so valuable. If every step becomes slightly less mechanically demanding, it can become easier to move more. That can create a positive cycle: less weight can make movement easier, easier movement allows more activity, and increased activity helps maintain strength and fitness.
Think about carrying a backpack
A simple way of understanding the mechanical effect is to imagine putting a 10 kg backpack on your back and wearing it all day.
You would notice it when standing up. You would notice it walking upstairs. You would notice it walking around the supermarket. You would notice it getting in and out of the car.
Now imagine carrying that backpack every day for years.
It isn't a perfect analogy because body weight is distributed throughout the body rather than carried in a backpack, but it gives an idea of the additional physical demand that excess body weight can create.
Research has also demonstrated that carrying additional external weight increases knee loading during activities such as walking and stair climbing. (PubMed)
The reverse is therefore encouraging: when you lose weight, you are effectively removing some of that additional load from every movement you make.
Weight affects joints in more ways than simply load
The relationship between obesity and osteoarthritis isn't purely mechanical.
Osteoarthritis is a complex disease involving the whole joint and surrounding tissues. Mechanical loading is important, but there are also metabolic and inflammatory processes associated with excess adipose tissue that may contribute to joint symptoms and disease progression.
This was demonstrated particularly well in the IDEA trial, a large randomised controlled trial involving 454 adults with overweight or obesity, knee osteoarthritis and knee pain.
Participants were divided into three groups: intensive dietary weight loss plus exercise, intensive dietary weight loss alone, or exercise alone. After 18 months, the diet-and-exercise group had lost an average of 10.6 kg, compared with 8.9 kg in the diet-only group and only 1.8 kg in the exercise group. (JAMA / PubMed)
The groups that lost weight experienced reductions in knee joint compressive forces and inflammatory markers. The diet-and-exercise group also had better pain and physical-function outcomes than the exercise-only group.
Interestingly, the researchers found a dose-response relationship: people who lost more weight tended to experience greater improvements in knee loading, pain, inflammation and physical function. (PMC)
This is important because it tells us that weight loss isn't simply about taking pressure off a joint. It can potentially influence several of the factors contributing to pain and reduced function.
You don't have to lose enormous amounts of weight
One of the biggest mistakes people can make is thinking that weight loss is only worthwhile if they can lose a huge amount.
It isn't.
NICE specifically recommends weight management for people with osteoarthritis who are overweight or living with obesity. Its guidance states that any amount of weight loss is likely to be beneficial, while losing around 10% of body weight is likely to provide greater benefit than losing 5%. (NICE)
For someone weighing 100 kg, losing 5 kg is already worthwhile. Losing 10 kg is likely to provide greater benefit.
This is why I encourage people not to look at the entire journey and think, “I need to lose 30 kg.” That can feel impossible.
Think about the first 5 kg.
Then reassess.
Another 5 kg may make another difference.
Weight loss before knee replacement
Weight management becomes particularly important if you are preparing for a knee replacement.
A knee replacement is a major operation, and your body needs to be in the best possible condition to deal with the operation and the rehabilitation afterwards. Before surgery, you ideally want to maximise your cardiovascular fitness, muscle strength, mobility, nutritional status and general health.
NICE recommends that people preparing for hip or knee replacement receive advice about preoperative rehabilitation, exercise, lifestyle, weight management and diet, with the aim of maximising functional independence and quality of life before and after surgery. (NICE)
There is also evidence that obesity is associated with increased risks following total knee replacement, including infection, wound problems, readmission and revision surgery. A large systematic review and meta-analysis involving more than 3.1 million total knee replacements found increased risks of several complications in people with obesity. (PubMed)
However, this needs to be put into context. Being overweight or living with obesity should not automatically prevent someone from having a joint replacement. NICE specifically states that people should not be excluded from referral for joint replacement simply because they have overweight or obesity. Surgical suitability needs to be considered individually. (NICE)
The message is therefore not “you must lose weight before you can have surgery.”
It is:
“If you can safely lose some weight before surgery, it is a valuable opportunity to improve your health and prepare your body for the operation and rehabilitation.”
Exercise when your joints hurt
This is where things can become frustrating.
You know exercise is important, but walking hurts. Standing hurts. Stairs hurt. You may therefore feel that the very thing you need to do is the thing your knee won't allow you to do.
The answer is often to change the type of exercise rather than stop exercising completely.
An exercise bike can be an excellent option. Your weight is supported by the saddle, and there is no repeated impact from your foot striking the ground. Start with low resistance and a duration that feels manageable. For someone who is very deconditioned, five or ten minutes can be a perfectly reasonable starting point.
As your fitness improves, gradually increase the duration or resistance. You don't have to start by cycling for 30 or 60 minutes.
Swimming and aquatic exercise can also be excellent. Water provides buoyancy, which supports part of your body weight and can make movement easier. Walking in water, swimming or attending an aqua exercise class can allow someone to work their cardiovascular system and lower-limb muscles while placing less weight through the joints.
You don't even have to be a particularly good swimmer. For some people, simply walking up and down a swimming pool is an excellent starting point.
Other options include cycling outdoors, cross-trainer work, seated cardiovascular exercise and appropriately prescribed strengthening exercises.
And don't forget strength training. Strong quadriceps, gluteal muscles and calf muscles are important for maintaining mobility and making everyday activities easier. Exercises such as sit-to-stands, step-ups, bridges, mini squats and resistance-band exercises can all have a role, depending on the individual.
NICE recommends therapeutic exercise for people with osteoarthritis, including muscle strengthening and aerobic fitness, tailored to the individual. (NICE)
But if weight loss is your goal, don't rely on exercise alone
This is an important distinction.
Exercise is extremely important for health, but it can be surprisingly difficult to lose substantial amounts of weight through exercise alone.
The reason is simple: it is relatively easy to consume a large number of calories but considerably harder to burn the same number through exercise.
The IDEA trial demonstrated this particularly well. The exercise-only group lost approximately 1.8 kg over 18 months, whereas the diet-and-exercise group lost approximately 10.6 kg. (PubMed)
That doesn't mean “don't exercise.”
It means use exercise for what it is brilliant at: improving strength, cardiovascular fitness, mobility, confidence and general health, while making dietary changes to create the calorie deficit required for weight loss.
The NHS similarly emphasises that reducing calorie intake is central to weight loss, while regular physical activity provides important benefits for health and weight management. (NHS)
Start with the supermarket
This is probably my favourite piece of practical weight-loss advice:
If you don't buy it, you don't eat it.
It sounds almost ridiculously simple, but your food environment has an enormous influence on what you eat.
If your cupboards are full of biscuits, crisps, sweets, cakes and chocolate, you're relying on willpower every time you walk past the cupboard. If you're tired after work or sitting watching television in the evening, that can become difficult.
Instead, make the decision in the supermarket.
Don't buy the family-size bag of crisps if you know you will eat it. Don't buy several large chocolate bars because they are on special offer. Don't fill the freezer with takeaway meals.
Buy foods that make the healthier choice easier.
The NHS specifically recommends not stocking unhealthy foods and suggests making healthier swaps instead. (NHS)
The supermarket is where a lot of weight loss starts.
You don't need a perfect diet
Weight loss doesn't mean that you can never eat pizza, curry, fish and chips, chocolate, cake or a nice meal out again.
For most people, that isn't realistic or desirable.
It is much more useful to think about what you eat most of the time.
You might keep your weekday food fairly simple and nutritious and have more flexibility at the weekend. You might have a takeaway once rather than several times. You might enjoy a dessert when you're out rather than automatically having one every night.
The NHS recommends reducing foods high in fat and sugar and paying attention to portion sizes, while building meals around vegetables, protein and higher-fibre carbohydrate foods. (NHS)
The goal isn't perfection.
The goal is something you can still be doing in six months and six years.
Think about swapping rather than banning
Completely banning favourite foods can make a diet feel miserable and can sometimes lead to an all-or-nothing approach.
Instead, look for simple swaps.
If you regularly drink sugary drinks, switch to water or fizzy water, tea, or coffee. Sugarfree alternatives are seeming to have negative health conseqneces, people finding the crave more sweet foods after sweet drinks.Could you swap to fizzy water and add a splash of fresh lime or lemon. If this is too tart, maybe a small dash of fruit cordial. If you regularly eat highly processed snacks, try fruit, yoghurt or a smaller portion of something you enjoy. If you have a large takeaway, consider whether a smaller portion or a homemade version could work.
You can also save richer foods for occasions when you really want them rather than eating them routinely.
The NHS advises reducing foods high in sugar and fat and making healthier swaps rather than relying on extreme dieting. (NHS)
A simple yoghurt and fruit swap
Yoghurt is a good example of where the supermarket can make a simple food surprisingly complicated.
Some flavoured yoghurts and yoghurt desserts contain significant amounts of added sugar, syrups or other sweetening ingredients. That doesn't mean that every flavoured yoghurt is unhealthy, and sweeteners are not automatically harmful, but it is worth checking the label rather than assuming something is healthy simply because it is sold in the yoghurt section.
The NHS recommends lower-fat, lower-sugar yoghurts and gives plain yoghurt as a good option. It also points out that lower fat does not necessarily mean lower sugar, because some reduced-fat products have added sugars. (NHS)
A simple alternative is to buy plain 0% Greek yoghurt or natural yoghurt and add your own fruit.
Frozen fruit is particularly useful. Keep a bag of frozen berries in the freezer and take a couple of spoonfuls out the night before. Put them in a container in the fridge and they will be ready to add to your yoghurt the following day.
Blueberries, raspberries, strawberries and mixed berries work particularly well.
Frozen fruit still counts towards your 5 A Day, so there is no need to think that fresh fruit is automatically better simply because it hasn't been frozen. (NHS)
Another simple option is plain Greek yoghurt with sliced banana and a small drizzle of honey. The banana provides sweetness and you only need a little honey for additional flavour. Remember that honey is still a source of free sugar, so it is best used as a small addition rather than something to pour generously over the yoghurt. (NHS)
The advantage of making the yoghurt yourself is that you know exactly what has gone into it. Instead of buying a strawberry-flavoured yoghurt and relying on the manufacturer to decide how sweet and strawberry-like it needs to taste, you start with plain yoghurt and add actual strawberries.
It is a small example of a much bigger principle: eat more food in its simpler, recognisable form and make the decisions yourself.
Don't be frightened of dark chocolate
If you have a sweet tooth, completely removing chocolate can be difficult.
One approach is to change the type and portion rather than trying to eliminate it altogether.
Moving from very sweet milk chocolate towards dark chocolate containing around 70–85% cocoa can be useful for some people. It still contains calories, so it isn't a weight-loss food, but the stronger flavour and lower sweetness can make a smaller portion more satisfying.
For someone who routinely eats a large amount of milk chocolate, a couple of squares of dark chocolate after dinner may be a much more sustainable approach than trying to ban chocolate altogether.
The important thing is portion size. Dark chocolate is still energy-dense.
The same principle applies to many foods: don't ask only what you can eliminate — ask what you can improve.
Ultra-processed foods: don't overcomplicate it
Ultra-processed food has become a major topic in nutrition, and it is worth being sensible rather than extreme.
Not every processed food is unhealthy. Processing includes everything from freezing vegetables to making bread, and foods classified as ultra-processed vary considerably in nutritional quality.
However, many highly processed foods are particularly easy to overeat. They can combine fat, salt, sugar and refined carbohydrates in ways that make them very palatable while providing relatively little fullness.
You don't necessarily need to identify every food according to a complicated classification system.
A useful starting point is simply to ask:
“Could I recognise most of these ingredients as food?”
Choose more vegetables, fruit, potatoes, oats, wholegrains, beans, pulses, eggs, fish, chicken, lean meat and plain dairy products. Reduce the frequency of foods that are very easy to eat in large quantities.
Again, the supermarket matters.
If you don't buy it, you don't eat it.
Protein matters when you're losing weight
Weight loss shouldn't simply mean making the number on the scales smaller.
You also want to preserve as much useful muscle as possible, particularly if you are older, have mobility problems or are preparing for joint replacement.
Protein-containing foods can help with fullness and provide the building blocks needed for muscle maintenance. Good options include eggs, fish, chicken, lean meat, Greek yoghurt, cottage cheese, beans, lentils and other pulses.
The NHS recommends including a source of protein at meals as part of a healthy diet. (NHS)
Combining adequate protein with resistance exercise is particularly useful. You are not simply trying to become lighter; you are trying to become lighter, stronger and fitter.
Don't underestimate sleep and routine
Weight management isn't just about food and exercise.
Poor sleep, stress, irregular routines and tiredness can all make healthy eating more difficult. When people are exhausted, convenience food and high-calorie snacks can become much more tempting.
Having a relatively predictable routine can therefore help.
Plan your meals. Shop with a list. Keep healthier foods available. Don't leave yourself ravenous at the end of the day.
You don't have to make hundreds of decisions every day if you make some of them in advance.
Think of weight loss as part of your joint rehabilitation
We often think of rehabilitation as exercises: strengthening the quadriceps, improving knee movement, practising balance and gradually increasing walking.
But if someone is carrying significant excess weight, weight management can be another part of rehabilitation.
Every kilogram lost potentially reduces the mechanical demand placed on the lower limbs. It may make walking easier, make exercise more achievable and improve general health. As fitness and strength improve, activity can increase further.
The cycle can become positive:
Lose some weight → move more comfortably → exercise more → become stronger and fitter → maintain or continue weight loss → move more easily.
Unfortunately, the opposite cycle can happen too:
Pain → less movement → reduced fitness → weight gain → greater joint loading → more difficulty moving.
One of the aims of physiotherapy is to help people break that cycle.
You don't need to wait until you are “thin”
Perhaps the most important message is that you don't need to reach an ideal weight before you start benefiting.
If you weigh 120 kg and lose 5 kg, you haven't failed because you still weigh 115 kg.
You've lost 5 kg.
Your body is carrying less weight.
Your joints are dealing with less load.
You've made a positive change.
Lose another 5 kg and you've made another positive change.
NICE specifically recommends explaining to people with osteoarthritis that any amount of weight loss is likely to be beneficial, with around 10% generally providing greater benefit than 5%. (NICE)
So don't focus entirely on the final destination.
Focus on the next 5 kg.
Then the next.
The bigger picture
Weight isn't the only cause of joint pain, and losing weight isn't a cure for osteoarthritis. Genetics, previous injuries, muscle strength, activity levels, joint structure, age and many other factors influence joint health.
But weight is one factor that you can potentially change.
And unlike some treatments, weight management can potentially benefit your knees, hips, cardiovascular system, blood pressure, metabolic health, fitness and general wellbeing at the same time.
If you have painful weight-bearing joints, particularly if you are considering a knee or hip replacement, even modest weight loss can be a worthwhile goal.
You don't need a perfect diet. You don't need to run. You don't need to spend hours in the gym.
Start with the supermarket. Make a few better food choices. Reduce the foods that are easiest to overeat. Find an activity your joints tolerate — perhaps cycling, swimming, aquatic exercise or appropriately prescribed strengthening. Build gradually.
And remember that every kilogram counts.
It isn't simply about weighing less.
It is about asking your joints to carry a little less, while giving the rest of your body a better chance to become stronger, fitter and healthier.
Useful resources
NHS – Healthy eating when trying to lose weight
A practical guide to building healthier meals, choosing protein, increasing vegetables, selecting wholegrains and reducing foods high in sugar and fat.
NHS – Tips to help you lose weight
Practical advice about making sustainable changes, food shopping, activity and realistic weight-loss targets.
NHS – Calories and weight loss
A useful explanation of energy balance and why reducing calorie intake is central to weight loss.
British Dietetic Association – Weight Loss
The professional body for UK dietitians, with evidence-based information about weight management and finding professional dietary support.
NICE – Osteoarthritis
The UK clinical guideline covering osteoarthritis, including exercise, weight management and joint replacement referral.
NICE – Joint replacement
Guidance on preparing for hip and knee replacement, including preoperative rehabilitation, exercise, lifestyle, diet and weight management.
Research – weight loss and knee loading
Messier et al. demonstrated the approximate relationship between weight loss and reduced knee joint loading during walking in people with knee osteoarthritis.
Research – the IDEA trial
A large randomised clinical trial demonstrating that dietary weight loss, particularly combined with exercise, reduced knee loading and improved pain and function in people with knee osteoarthritis.
Research – obesity and knee replacement
A large systematic review and meta-analysis examining complications following total knee replacement in people with obesity.
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