A simple collection of information on how losing weight and fat works.
How We Gain Weight`
Our bodies gain energy from the food we eat, storing this energy mainly in fat cells around the body and as glycogen in muscles.
While a generalization, the basic rule is that we put on extra weight if our energy intake (measured in calories) is bigger than our energy output.
How We Lose Weight
Spending Energy
We burn the energy in three ways:
- base metabolism (resting expenditure) - the energy needed for the body to function
- eating - energy spent to digest and metabolise food
- activity expenditure - the energy spent on movement
Losing Weight
To lose weight we need to burn more calories than we eat.
Recommended calorie deficit is usually 300-500. It needs to be revaluated often
- To calculate calorie deficit, calculate the resting metabolism
The main two ways to achieve and control that balance is increasing the amount of activity by exercising and reducing the caloric intake by dieting.
Aside from that the quality and quantity of our sleep and the amount of stress we experience are the most influential factors.
Other factors include: hormones, medication, health conditions and genetics
Dieting for Weight Loss
When we diet our bodies use the fat reserves because of the deficit in energy.
There are many diets said to be miraculous for weight loss but those naturally don’t work reliably, and extreme diets can lead to their own set of problems. While stricter diets may be more effective in achieving quick gains, their unsustainability over longer periods can lead to regaining the lost weight.
The most popular stance is that a sustainable diet which includes permanent change of eating habits is the best. Healthy elements of known diets such as Mediterranean, DASH, MIND and Scandinavian diets are:
- unprocessed products
- plant-based ingredients
- low-sugar
- low-fat
Another popular practice is intermittent fasting (for example having a daily food window), which is known to be beneficial, but not proven to be better than keeping a good diet and limiting afternoon/evening food intake. An important point when considering intermittent fasting is social interactions interfering with the practice.
Activity/Exercise
In context of weight loss exercise can be beneficial in two ways:
- Gaining muscle mass - increases the base metabolism - weight/resistance training
- Burning fat - increasing the activity expenditure - aerobic training
When exercising, the glycogen in our muscles is used before the fat, which only begins to be burned after 30-60 minutes of aerobic training (60 when exercising moderately).
The recommended amount of exercise for weight loss is 150-200 minutes per week or 30-50 minutes per day of both resistance and aerobic training.
The Process
Usually weight loss proceeds in a two stage process: the initial quick phase where the body loses a lot of weight from stored water, and second slower phase where the fat is burned.
Weight loss is also not equal to fat loss because it includes weight loss from water and muscles, which can be detrimental.
The process of burning fat releases carbon dioxide expelled by exhaling and water expelled by urine and sweat. An important note is that when we lose weight our fat cells shrink but are not destroyed which causes the weight to be easier gained a second time.
Sustainability
To make weight loss permanent and prevent the gains from disappearing we have to commit to behavioural and lifestyle changes.
The mechanisms that make it difficult for our weight to continue dropping / stay low are:
- metabolic compensation - metabolism slowing down when we’re losing weight
- hormone response - producing more leptin (feeling of being full) and more ghrelin (feeling of hunger)
- brain function altering - not noticing how much we eat
Moreover some people may encounter emotional problems during the process, for example if the weight loss results in a figure that is different than they imagined it to be. It’s important to realize that losing weight in itself will not bring us happiness change how we feel about our bodies.
It may help to plan weight loss in a way that includes social support, for example a ‘buddy’
Sources
https://www.health.harvard.edu/topics/diet-and-weight-loss
https://www.nm.org/healthbeat/healthy-tips/how-your-body-fights-weight-loss
https://www.nature.com/articles/ijo2012109
https://health.clevelandclinic.org/where-does-body-fat-go-when-you-lose-weight
https://www.technologyreview.com/2022/10/20/1061254/where-does-weight-loss-go/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3225890/
https://pubmed.ncbi.nlm.nih.gov/19127177/
https://www.healthline.com/nutrition/where-does-fat-go-when-you-lose-weight
https://www.healthline.com/nutrition/weight-loss-stages
https://www.healthline.com/nutrition/calorie-deficit