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What causes rapid weight gain?

5 unexpected causes of weight gain

Weight gain is typically associated with eating too much and not doing enough exercise - but there have been many studies which suggest there are more factors at work.

Last year, Marsden published this blog post highlighting 10 things your doctor wishes you knew about weight loss.

It highlighted the effects stress and a lack of sleep can have on your weight.

But what other things that might not have crossed your mind may be influencing your weight loss efforts? Marsden investigates.

What causes rapid weight gain?

Common causes for weight gain which are not related to medical conditions are:

Increase in food consumption

According to the NHS ‘most people put on weight because they eat and drink more calories than they burn through every day and movement and body functions’. The European Association for the Study of Obesity reported in 2009 that the rise in obesity since the 1970’s was almost exclusively caused by an increase in calorie intake.

Reduced physical exercise

A reduced amount of exercise is seen as the main reason weight gain occurs as we get older. Some calories are burned while we eat, but the majority of energy expenditure occurs during and after exercise, known as physical-activity expenditure and post-exercise oxygen consumption. As we get older, we exercise less.

Water retention

Unexplained rapid weight gain may be the result of fluid retention which can cause your limbs, hands, feet or face to look swollen - according to Healthline.

Stress, depression and anxiety

Weight gain can be a symptom of anxiety - but anxiety doesn’t always cause weight gain. The stress hormone cortisol is the key reason why people with anxiety have trouble managing their weight. Cortisol is released during times of stress, and causes fat to build up. Stress and anxiety can lead to excess eating. People find that food provides a valuable coping tool and some people experience greater hunger when stressed.

Lack of sleep

Rapid weight gain can be caused by sleep deprivation. Research from the University of Colorado found that one week of sleeping about 5 hours per night led to participants gaining an average of 2 pounds (0.9kg). Sleep deprivation causes changes to hormones that regulate hunger and appetite. It can also affect food craving, stipulating in more intense cravings for fat and sugar-laden foods. People may also turn to food if they cannot sleep.

Meal times

A recent study has shown growing evidence between eating later in the day and weight gain. Earlier studies have identified a pattern between eating later and increased weight gain, with “calorie intake after 8pm increasing the risk of obesity.” Those who ate later in the day had a higher BMI and greater levels of body fat. The research also showed that those who ate later in the day still had an average of 7 hours sleep, which implies lack of sleep is not the primary driver of these effects.

Medical reasons for weight gain

As well as the reasons above, rapid weight gain can be caused by medical reasons, highlighted by the NHS.

Underactive thyroid

This means your thyroid gland is not producing enough thyroid hormones - which plays a central role in regulating metabolism. “Without enough thyroid hormone, the body’s metabolism slows down, which can lead to weight gain,” says dietitian Catherine Collins.

Diabetes treatment

A common side effect for people who take insulin to manage diabetes is weight gain. Insulin helps to control blood sugar levels, with some people with diabetes tending to eat more than they need to prevent low blood sugar level.


People begin to lose amounts of muscle as they get older and become less active. A loss of muscle mass can mean you burn fewer calories.

Steroid treatment

Steroids, known as corticosteroids, are used to treat a variety of conditions. Long-term use of corticosteroid tablets can increase appetite in some people. “Steroids make you feel hungry as they affect areas of the brain that control feelings of hunger and satiety,” says Collins.

Polycystic ovary syndrome (PCOS)

This is a common condition that affects how a woman’s ovaries work. The cause of PCOS is unknown, but it is thought to be hormone-related, including too much insulin and testosterone. “Women with PCOS typically put on weight around their waste. The more weight you put on, the more insulin you produce, which can cause further weight gain,” said Collins.

Regular weighing helps prevent weight gain

Weighing regularly can prevent weight gain, according to experts at the University of Birmingham and Loughborough. The research compared two groups - one that was instructed to record their weight and one that was not - in a goal to not gain weight.

The group that was not recording their weight gained 0.37kg on average during the study; those that were recording weight lost 0.13kg.

To reduce the obesity epidemic, the government has also recommended patients are “weighed by default” when visiting a GP.

5 unexpected causes for weight gain
1. Your personality

This blog post by Marsden in 2016 found that certain weight trends are more commonly associated with certain personality types.

Extroverts believe they are leaner and thinner than they actually are, according to the study. Meanwhile, weight gain is more common among people who are impulsive and those who enjoy taking risks - which are traits associated with being extroverted.

“Impulsive individuals are prone to binge eating and alcohol consumption,” said Angelina R. Sutin, from the National Institute of Aging. “These behavioural patterns may contribute to weight gain over time.”

2. Being a night owl

People who go to bed late eat more calories in the evening, according to a Northwestern Medicine study.

The study found that late sleepers consumed 248 more calories a day, twice as much fast food and half as many fruit and vegetables as those with earlier sleep times. They also drank more full-calorie sodas.

“The extra daily calories can mean a significant amount of weight gain - two pounds (0.9kg) per month - if they are not balanced by more physical activity,” said co-lead author Kelly Glazer Baron.

3. Being embarrassed

A study by WW (formerly Weight Watchers) has found 80% of men are embarrassed for choosing soft drinks and diet options when they are with their friends.

Almost 90% of the 2000 people surveyed said they want to lose weight in 2019 - but 80% will likely fail to achieve this goal.

60% of men also said that they need their partner to motivate them into losing weight.

4. Your emotions

Emotional eating is a strategy when people are unable to effectively regulate emotions - emotional dysregulation.

Being unable to identify and describe emotions increases vulnerability to depression and anxiety, according to the Independent. This increases the chances of a person reacting without thinking - meaning they are more likely to turn to food to alleviate their feelings.

5. Your lifestyle changes

When it comes to managing weight gain, small changes in lifestyle can make a big difference.

If you have changed your lifestyle - perhaps by moving house or changing job - your routine becomes disoriented. Things like this can contribute to less walking, a change in diet and the amount of sugary drinks you consume.

“People might not realise that they’re eating all day long or that they’re consuming high-calorie drinks,” says Wendy Bennett, MD, MPH.

For more information on weight gain, you can read the NHS’ causes of obesity here.

Why you should regularly weigh yourself

Regular weighing can help you to spot fluctuations in weight. Use accurate professional medical scales to ensure consistency and accuracy in weight results - which cannot be demonstrated in the cheapest bathroom scales. Weight can fluctuate during the day, so it is worth being consistent with the time of day you are weighing.

For patients with obesity, issues can be identified sooner. According to the Government, all GP patients should be “weighed by default”. In hospitals, patients should be weighed on admission.

Weighing scales to use

The Marsden M-150 is a robust, affordable column scale. Perfect for gyms, sports clubs and leisure centres, it has a high 300kg capacity suitable for almost every user.

The Marsden M-550 is a Class III Approved weighing scale - suitable for anyone who weighs themselves at home regularly, as well as GP surgeries. It is our lowest priced Class III medical scale and can be used as a bathroom scale.

For greater accuracy, important for hospital weighing, the M-420 Floor Scale weighs in increments to 50g when weighing below 150kg. A robust and easy to use scale, it is lightweight enough to be carried between wards, and a carry case is available.

For more information on any Marsden weighing scales, call 01709 364296 or contact us here.