What causes Obesity – the test of time?

1. The main suspects

Many causes of obesity have been suggested. The most popular is eating too much and moving too little.

Other suggested causes include our genes, some medical conditions (like an underactive thyroid gland), some medications (like some anti depressants), emotional factors, age, alcohol and lack of sleep.

2. The test of time

One useful check for any suggested cause is the test of time. What has changed significantly since the early 1980’s, when obesity rates first began their rapid rise in the UK, which might potentially explain that rise?

For example:

  • Human genes are unlikely to have changed significantly since the 1980’s.

There may be a sub population with a pre existing genetic predisposition to excess weight when food is plentifully available – but if so, it is the unprecedented availability of calories which is the trigger.

  • The fact that humans age and grow old isn’t new. It has been true throughout human history.
  • Levels of unhappiness, stress and depression among adults don’t seem to have risen significantly (despite media suggestions to the contrary). For example suicide rates have fallen.
  • It is unlikely that medical conditions like an underactive thyroid have become more common. And research suggests that it is the obesity which triggers thyroid problems rather than the other way round.  
  • Overall levels of physical activity have remained about the same. Work may now, on average, be more sedentary. However there has been an increase in leisure time physical activity – as seen in increased gym membership and the increased participation in marathons and fun runs.
  • While some research has suggested that lack of sleep is a factor, international sleep surveys show no obvious correlation between length of sleep and obesity levels in the different countries – suggesting that other factors are more important.
  • There has been a dramatic increase in anti-depressant prescriptions (as opposed to diagnoses of depression) – and anti-depressants are known to increase the risk of weight gain. However, the most rapid increase in prescriptions occurred when levels of obesity were levelling off, suggesting this may be a factor for some individuals but is not a significant factor overall. 

3. The test of time – is alcohol a possible factor?

  • Alcohol consumption rose during the 1980’s and 1990’s but has since fallen back over the last ten years or so. This roughly correlates with obesity levels which rose during the 80’s and 90’s but have since begun to level off (but not fall).

Alcoholics are rarely overweight, as they tend to neglect eating and the alcohol affects the way their liver digests food. However, regular alcohol consumption alongside food tends to add ‘hidden calories’ so is a possible contributory factor.

4. The test of time – What has changed significantly?

  • What we eat and drink, when, where and how have all seen significant changes since the early 1980’s, so could be a potential cause.

Examples include significant increases in:

-      The availability and consumption of carbonated drinks and snacks (often consumed in addition to the main meals of the day)

-      Ready meals (following the introduction of the microwave in 1984)

-      Takeaways and meals in fast food outlets (now a £30 billion a year market in the UK). 

What these trends have in common is a rise in food which is calorie rich but nutritionally poor (and often relatively cheap and widely available) - potentially leading to people becoming overweight but undernourished.

5. Research findings

Research is increasingly confirming that, although exercise has many health benefits, it is what people eat and how much which is primarily causing obesity – with factors in the early months and years of life also important.

The key points here are that:  

Food high in sugar, salt, fat and refined carbohydrates is particularly likely to lead to weight gain.

This appears to be because:

  • They are calorie rich (so you consume more calories for a given volume of food)
  • They don’t make you feel full for long (increasing the risk of overeating)
  • Where sugar is concerned this may be ‘hidden’ (so people don’t realise how much they are consuming)
  • They don’t contain much fibre (which could help control weight) and they reduce the diversity of our gut microbiota (which is now being suggested as an another factor influencing weight).
  • Where such food is relatively cheap and readily available this is likely to be a further factor leading to overconsumption.
  • Salt contributes to weight gain in a different way. It increases thirst, leading to increased fluid consumption – and where the fluid is sugar sweetened beverages this contributes to weight gain as described earlier.

Conversely vegetables, fruit and whole grains are particularly likely to help control weight.

This appears to be because they are pretty much opposite in the way they work i.e. they

  • Are not so calorie dense
  • Make you feel fuller longer
  • Don’t containing hidden ingredients likely to increase weight
  • Contain fibre and encourage more diverse gut microbiota.

As regards the early months and years of life a range of interventions were proposed by Professor Mary Rudolf, in order to help tackle obesity, based on her review of the research i.e.

  • Encourage responsive feeding.
  • Encourage positive family mealtimes
  • Find alternatives to food for comfort and to encourage good behaviour
  • Encourage exclusive breast feeding for 6 months
  • Introduce solid foods at 6 months
  • Ensure portion sizes are appropriate for age
  • Increase acceptance of healthy foods – including fruit and vegetables
  • Reduce availability and accessibility of energy dense foods in the home
  • Reduce consumption of sweet drinks and increase consumption of water

These again focus on the importance of food but shift the focus to the earliest months of life, when food tastes, habits and preferences are being established. 

Some researchers would start the process even earlier. They argue that what mothers eat when they are pregnant and how much and whether or not they themselves are obese has significant influence on how their baby will develop.   


Research findings and the test of time agree on the key points:

  • A diet high in sugar, salt, fat and refined carbohydrates increases the risk of obesity.
  • A diet rich in vegetables, fruit and whole grains reduces the risk of obesity.
  • Exercise has many health benefits and can help manage our weight - but what we eat and how much we eat is even more important.
  • The first thousand days of life (from conception onwards) are particularly important in establishing food tastes, habits and preferences – meaning parents have a particularly important role to play.