How much fat can we lose in a week?

During my research and review of the available literature, the highest reduction I have found in adipose tissue, our fat stores, is 3.5lbs (1.6kg) over the course of a week. This was in a laboratory controlled environment and included nearly complete starvation. Yet, marketing for weight loss products often states that we can lose far more than this, sometimes in just a few days. How can this be?

Our metabolism can only work ‘so fast’. Metabolism is the amount of chemical reactions taking place in our body. This limits how much fat can be released to be utilised as energy over a given time. There are physiological and biochemical limiters at play. 

I would suggest that the most fat a person can realistically look to lose over the course of a week would be 1-2lb, or around 0.5-1kg. Any other weight loss over and above is unlikely to come from fat. Instead it will come from other sources. These will be our carbohydrate stores, water retention, muscles being eaten into for energy - together with our daily fluctuations in how much food and waste is in our digestive system, our hydration levels, and our general water retention.

Key points:

• The maximum ‘fat’ we can lose in a week is around 3.5lbs (1.6kg)
• The realistic figure for how much fat we can expect to lose in a week would be 1-2lb (0.5-1kg). 
• Any more weight loss will be water, carbohydrate stores, muscle mass and daily fluctuations in our digestive tract and water retention.

Our body has carbohydrate stores to fuel physical activity and our blood sugar levels. These stores are in our muscles and liver, and we store the carbohydrates in the form of glycogen. For every 1g of glycogen we store, we also store around 3g of water as part of the process.

As we diet our carbohydrate stores may reduce, which also releases the stored water. Depending on our physical activity and food we will also probably be eating into our muscle mass to use it as fuel. Let me illustrate the carbohydrate point further by showing just a bit of what happens under starvation.

In total starvation, within around 24 hours our livers run out of their stores of carbohydrates. (The liver maintains blood sugar levels, and has a store of carbohydrates from which to do this.) There is about 100g of carbohydrate in our livers and this is stored with around 300g of water. So in 24 hours we may lose around 400g of weight from the reduction in carbohydrates in our liver.

At the same time we will be depleting our muscle carbohydrate stores, which account for more by way of carbohydrate and water weight. Just accounting for the reduction in carbohydrate and water from the muscles and liver can account for a 1kg reduction in weight during the first day of starvation alone. When moment we eat carbohydrates again the stores start to be replenished and the water is again retained. This is therefore an element of ‘transient’ weight loss.

Our blood sugars have to be maintained within variable tolerances. So as the blood sugar drops our liver replenishes the blood sugar from its glycogen stores. Yet, when they are depleted we still need energy. So the muscles start to be broken down and the liver converts these proteins to sugar, to maintain our blood sugar levels. We eat into our muscles, therefore losing more weight. 

Key points:

• In around 24 hours of total starvation we may lose 1kg in weight from carbohydrate and water. 
• This is transient weight loss and will be replaced when we are eating again. 
• With our livers depleted of carbohydrate we start to eat into muscle giving weight loss we don't need.

 When starting a fat loss regime initially there can be some high levels of weight loss. Yet, be aware, most of this weight will NOT be fat. Much of the weight loss will be water and carbohydrate, which represents transient weight loss. We'll put this straight back on when we begin eating again. We may also be eating into our muscles to use them as energy - and this is weight loss that is not beneficial.

In order to lose fat a careful approach is required, and it is not an easy task. It is not simply a matter of eating less and exercising more. We need to balance our hormonal responses to food. Exercise and physical activity needs to be targeted towards using fat as a fuel source. A person’s psychology needs to adapt to take on board life changes and knowledge, so that behaviours can change. 

A person looking to drop fat also needs to understand that whilst reducing the energy absorbed v the energy expended may have initial success, long term the body will look to regain the weight loss – and due to ‘metabolic damage’, possibly add more weight. This results in studies showing that 95% of people who start a calorie restrictive diet end up larger after a year.

To lose fat, and keep it off, is an art form, one that I teach in my workshops and will also present in the products I have in development. Short term approaches are needed and also long term approaches – and it is likely that both approaches will require different approaches. Everything also needs to be tailored to an individual.

Be aware of marketing in weight loss products. Please take heed of the information I have written here, and be better informed. Realistically the total amount of fat we can expect to lose in a week is 0.5-1kg, and that is probably under optimum conditions. Any claims stating that more fat than this can be lost in a week are most probably very ‘questionable' at best.