What is a healthy rate of weight loss?
She lost weight SO fast. It must all be fluid right?
I’m only losing a few hundred grams; does it need to happen faster?
If I lose weight too quickly, will that mean I am losing muscle?
These are questions that I discuss with clients on a regular basis. There are lots of confusing recommendations out there about how fast or slow you should lose weight, which can be super confusing.
Based on the research, the 1998 clinical guidelines outline a reasonable rate of weight loss as anywhere between ¼ kg – 1 kg of body weight per week. This average is based over a 6-month period. As you can probably see, this is a very big range. In a 6-month period that could mean anywhere between 6 and 24kg of weight.
The rate you lose weight depends on quite a few things:
- Your initial body weight.
- How much of an energy deficit you are creating.
- How long you are following a particular diet and exercise pattern
Your weight at any given moment is a composition of MANY different things and they are ALL changing at different rates. So, when you jump on the scales each week, in the nude and after a wee or a poo (don’t worry, you’re not alone), there are actually lots of things that effect how much change you will see on a week-to-week basis.
First, let’s understand what’s making up that weight number and how much that might be contributing to the rate of weight change:
Organs and bones
All of your organs have mass. Your brain weighs about 1.2 kg, your lungs weigh about 1 kg, your intestines weigh about 3.5 kg (not including your poo) and your spleen weighs about 140g. Amazingly, your skin can weigh 10kg or more!! When you add all of these things together, your organs make up a large proportion of your body composition.
Your bones are also contributing to your weight, but compared to your organ weight it’s actually much less. The bones of a man weigh about 2.5 – 3.5kg and the bones of a woman weigh about 1.5 – 2.5kg.
Altogether, your organs and bones can weigh upwards of 20kg. The weight of your organs and bones depends on genetics, environmental factors and different diseases. (Note: once you’re an adult your organ and bone weight stays quite stable day-to-day and year-to-year). It takes very drastic and consistent change to see weight change coming from your organs and bones.
Fluid volume
A HUGE proportion of your weight is made up of water! The research suggests that it can be up to 75% of your body. But, because your body is constantly sweating, peeing, drinking, and storing water, at any given moment your fluid volume can change dramatically. This can have a significant impact on your weight and the apparent rate of weight change.
You might jump on the scales first thing in the morning and weigh yourself. Then you have a cup of coffee and a few sips of water and weigh yourself again and you are up 400g. Then you go about your day in the hot weather, drinking bottles of water, going to the toilet a few times and then at the end of the day you are up another 300g. Then you get up in the morning and compared to last night you are down 500g but compared to yesterday morning your up 200g.
Glycogen and fluid storage
A very important contributor to this variation is our storage of fluid, which is highly influenced by glycogen. When you eat carbohydrate or sugar rich foods, your body stores that for short term use in the muscle and the liver as a compound called glycogen. To build this store of glycogen you need water. So when you have a day with more carbohydrates, your glycogen storage increases and your fluid volume increases and so your weight increases. Or if you have a couple of days of less carbohydrates your body uses up it’s stored glycogen and excretes the fluid it was storing, so your weight drops.
These fluctuations happen rapidly (within a few hours or day-to-day), so your fluid volume can easily skew our perception of how fast weight is changing
Bowel contents
Similar to your fluid volume, the amount of food and poo in your bowels has dramatic impact on your weight measurements. It takes anywhere from 8 to 48 hours for food to move all the way through your gastrointestinal track and the volume of fibre you eat will influence how much it weighs when comes out the other end.
The fluctuations in your bowel contents can cause a change in your weight day-to-day and week-to-week.
Muscle
Your muscle is a big contributor to your weight and is a component of your body composition that will change as you try to lose or gain weight.
We can increase the weight and mass of our muscle through the combination of 2 keys:
- Regular resistance exercise
- Adequate energy and protein intake
Because weight loss requires you to be in an energy deficit, it’s often difficult to build muscle as you lose weight. In fact, losing weight often results in losing some muscle mass. The process of breaking down muscle takes time and effort and some metabolic adaptations, so a true reflection of muscle loss and gain can take weeks or month.
Body fat
Finally, we are getting to the one that you want to see change when you’re trying to lose weight.
Body fat is our long-term storage of fuel. Our body has taken advantage of all the times that we have eaten more than we need and it stores that energy for times when we’re not getting enough.
However, fat is a very efficient form of stored fuel, so when we do create an energy deficit, we don’t need to use very much fat to keep our body running. For instance, 100g of body fat provides 900 calories of energy, which is enough to fuel a person for 22,500 steps (based on an 80kg adult). That’s pretty efficient!
As a result, losing ¼ – 1kg of body fat change can take many weeks of consistent energy deficits.
Based on all of this information, you can start to see that the 500g weight change you notice in a given week is not just body fat change. It’s a fluctuation of MANY different parts of your body.
Play the long game
It’s really important to remember that the rate of weight loss outlined in the clinical guidelines is an average over 6 months. It’s very common for weight to change at different rates within that window of time. You may lose 2kg in the first week, 1kg in the second week, increase by 500g in the third week and stay stable in the fourth week. Over that month, that’s a total weight loss of 3.5kg and an average of 625g/week for that month. That’s perfectly healthy and within reasonable range.
This is why it’s not worth worrying too much about the rate of weight loss on a daily or even a weekly basis.
Putting weight change into the context of 1 month, 6 months or even 12 months, gives you a far better picture of the impact of your food and exercise habits on your body composition.
Is slower better?
So, is there a benefit to losing weight quickly (1kg/week) or more slowly (¼kg/week)?
The short answer is no, not really. Losing weight quickly over a short period of time and losing weight slowly over a longer period of time appear to have the same health and metabolic benefits. The rate of weight loss seems to be less important than:
- The total amount of weight (and particularly body fat) lost
- The maintenance of that weight loss
In that case, you can consider your weight loss approach under 2 scenarios:
Scenario 1
You decide you want to see some quick and significant results. You make lots of big changes to your lifestyle all in one hit. You:
- cut out sugar,
- cut out carbohydrates,
- restrict your calories
- exercise for an extra hour everyday
With these changes you might lose weight quickly. It’s likely that the initial change will come from a loss of glycogen storage and water and that given time, body fat mass will decrease along with some muscle loss. However, the weight and body fat changes that you see will only last as long as you keep up those patterns of eating and exercising.
If these big changes don’t fit into your life, you won’t be able to stick with them. As you return to your normal patterns of eating (including sugar occasionally, including carbohydrate, not tracking your calories and exercising in your normal routine), your weight is likely to increase. So to keep weight down, you have to restart those changes you initially made.
Scenario 2
You make small changes to your eating habits and patterns of exercise. You:
- reduce the number of sweet treats in your week
- measure out your serves of carbohydrate at dinner
- start taking the stairs 2 times a day
These changes might not bring about much change to your weight initially but over a month, you might notice that your weight is down a little bit. With practice these things become part of who you are and how you go about your day. You then have capacity to make further small changes like:
- measuring your serves of carbohydrate with breakfast and lunch
- planning your snacks for the week
- becoming more aware of your alcohol intake
If these things feel easy, they become part of your decision making and then over 6 months you have lost weight. Not as much as if you had been more strict, but by doing things that you can keep doing for the rest of your life.
Which scenario do you think will work best for you?
The bottom line
The measure of your weight is summing up a LOT about what’s happening in your body and changes to weight can be driven by all sorts of physiological fluctuations. It takes time to see a true change in body fat and muscle mass and an average measure of weight change over months is most accurate. Ultimately, it’s not how quickly you lose weight that’s important, it’s whether what you’re doing to lose weight is something you can keep doing … indefinitely.
If you would like support managing your weight in a way that is effective and sustainable, our team are here to help!
References
Coutinho SR, With E, Rehfeld JF, Kulseng B, Truby H, Martins C. The impact of rate of weight loss on body composition and compensatory mechanisms during weight reduction: A randomized control trial. Clin Nutr. 2018 Aug;37(4):1154-1162. doi: 10.1016/j.clnu.2017.04.008. Epub 2017 Apr 25. PMID: 28479016.
Jennifer L. Kuk, Rebecca A. G. Christensen, Sean Wharton, ”Absolute Weight Loss, and Not Weight Loss Rate, Is Associated with Better Improvements in Metabolic Health”, Journal of Obesity, vol. 2019, Article ID 3609642, 2019. https://doi.org/10.1155/2019/3609642
NHLBI Obesity Education Initiative Expert Panel on the Identification, Evaluation, and Treatment of Obesity in Adults (US). Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report. Bethesda (MD): National Heart, Lung, and Blood Institute; 1998 Sep. Available from: https://www.ncbi.nlm.nih.gov/books/NBK2003/
