Eat less, exercise more – a simple axiom for shedding those kilos.

But how much of weight loss is actually due to dietary control and how much to exercise?

Many people tend to assume it is a 50:50 ratio.

After all, it is all a matter of input and output, isn’t it?

Humans get their energy solely from food, and expend this energy through physical activity and physiological processes within the body.

Our weight is a balance between these two elements: eat more than you expend and you will gain weight, eat less and you will lose weight, and eat as much as you expend and you will maintain your weight.

It is a straightforward equation that assigns equal responsibility to diet and physical activity when it comes to weight control.

However, our body – and mind – is a complex and complicated organism that belies such a simple formula.

Restraint versus workout

The fact is, burning calories is far more difficult than consuming them.

For example, the average 50g chocolate bar would take about 70 minutes of active house-cleaning, 24 minutes of running or 55 minutes of walking, to burn for someone weighing 80kg. And that’s just to maintain your weight after having one chocolate bar!

Compare that to the effort needed to decide not to eat the chocolate bar in the first place – a bit of mental energy for a few seconds, maybe a minute, and you’re done.

And how about actually losing weight?

To lose half a kilogramme of body weight in a week, you have to burn around 3,500 calories – or 500 calories a day – more than you consume.

If you wish to get rid of these calories purely by exercising, this means that you have to add on, for example, two hours of active house-cleaning, 42 minutes of running or 90 minutes of moderately-brisk walking to your daily routine.

READ: Cut calories by thinking before you eat

Conversely, cutting out items like a Big Mac or two bars of chocolate or two slices of a regular-sized pizza – which each contain around 500 calories – from your regular diet will perform the same function.

Most would probably agree that the latter is more achievable than the former.

This is why the 80/20 Rule assigns an 80% weightage to diet and only a 20% weightage to exercise when it comes to losing weight.

This concept is backed up by research, which has shown that increased exercise alone gives little or no effect on weight loss, while dietary modification alone can produce significant weight loss.

In addition, many of us tend to underestimate how much we eat and overestimate how much we move.

“When people are confronted with how much they have eaten in a week, they are always incredibly surprised,” says Prof Dr Simon Griffin, who heads the Prevention of Diabetes and Related Metabolic Disorders Programme at the United Kingdom Medical Research Council (MRC) Epidemiology Unit based at the University of Cambridge.

This might be due to the fact that many of the reasons people eat are not due to conscious decisions, according to Prof Dr Susan Jebb, a member of Public Health England’s Obesity Programme Board.

Prof Jebb, who is also a professor of diet and population health at the University of Oxford, says: “In the moment, if you like the look of something to eat, why wouldn’t you eat it? It’s a perfectly reasonable thing to do.

“People don’t stop and reflect and think about it; they have chosen something to eat half-an-hour before they give it conscious thought.” (See Think when you eat)

And when it comes to the recommended 30 minutes of moderate activity a day, Prof Griffin says: “In fact, probably less than 10% of people do that if you measure them objectively.”

However, if people are asked to report on their own physical activity, this number increases to about 30%, reflecting the tendency to overestimate the amount of physical activity we do.

Keeping it off

This, of course, does not mean that we should forget about physical activity altogether when it comes to weight management.

Prof Griffin explains that while physical activity is not effective at producing weight loss, it is good for maintaining weight loss and preventing weight gain.

“If you want to achieve weight loss in people who are already overweight, you generally have to restrict calorie intake.

“And then, the increasing energy expenditure makes it easier to balance your energy in and energy out; and it helps maintain weight loss and prevent weight gain,” he says.

In addition, he explains that more physical activity is good for us, independent of losing weight.

“In general, it reduces your risk of heart attack, cancer, dementia, all sorts of nasty outcomes, but that’s not necessarily through its impact on weight.”

However, contrary to popular belief and practice when it comes to weight loss, he points out that exercise or sports is not how most people burn their excess energy.

“Few people get most of their energy expenditure from sports,” he says.

“For most people, it is everyday energy expenditure, like walking, climbing the stairs – that sort of thing.

“Sports isn’t really a solution to diabetes and obesity.”

Director of the UK MRC Epidemiology Unit and of the Centre for Diet and Physical Activity Research (Cedar), Prof Dr Nick Wareham, agrees.

The dialogue on physical activity, he says, is all about sports. “The problem is not of a deficiency in sports or exercise; the problem is one of a deficiency in physical activity.”

He explains: “I feel that, in a way, our successes (in modernisation) engineered physical activity out of our lives.”

Jobs have not only become more sedentary in nature, but even those that require physical activity need less of it due to mechanisation.

At home, appliances and devices are designed to save us not only time, but also physical activity, he says.

Travelling or moving about from place to place has also become a sedentary activity, involving sitting in vehicles, rather than an active one like walking or cycling.

So, while things like going to the gym, playing sports or brisk walking are healthy activities in general, embracing daily physical activity like the Health Ministry’s 10,000 Steps a Day campaign, is what will really help keep those kilos off.


Tan Shiow Chin was a 2015 Khazanah-Wolfson Press Fellow at Wolfson College, University of Cambridge. This article is part of a series from her fellowship project on the subconscious cues that influence us to eat more and unhealthily. Her next article will be on the influence of evolution on our eating habits.