The most common reasons you're not losing weight

You're not sleeping well

When we sleep our bodies naturally slow down and use less energy. It's quite amazing really how our bodies can do that. You might sleep for ten hours and feel fine in the morning. But try not eating or drinking for the same amount of time. You'd be thirsty and hungry, right?

If you're having trouble sleeping, then your body tends to go into stress mode. Stress hormones such as cortisol are naturally low at night, but will go up again if we're awake. Cortisol makes our bodies lay down fat reserves 'just in case'.

Plus if you're awake, you're up and probably in the kitchen. So your tendency to snack is higher.

The underlying question is: why aren't you sleeping? Which leads us on to ...

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You're feeling anxious, stressed or depressed

Nutritionist Sarah Walford, who runs the NW3 Nutrition clinic in London, explains: "Stress is a two-fold process. Some people feel so anxious they can't eat; others tend to binge eat. When you feel stressed, your body releases cortisol in an attempt to free up sugar into your bloodstream. If you then can't burn off that sugar it gets converted to fatty acids, which makes you put on weight. That kind of weight gain is often around the abdomen rather than the arms or legs."

You know that guy in the office with a really big belly but skinny arms and legs? Think stress.

Scientists have also found a potential link between carbohydrates and serotonin, the hormone that helps to regulate our moods. There is a theory that, without realising it, by eating carbohydrates we are attempting to boost our serotonin levels when we feel depressed. Hence why we love 'comfort food' when we're feeling down: pizza, mashed potato, toast! But of course, all that carbohydrate can make you put on weight.

You're working night shifts or long hours

Walford explains: "Many more people these days work through the night. Think nurses, factory workers, delivery drivers, office cleaners. Your body wants to be asleep, but if you're awake and working then your cortisol production kicks in. This is the same bad cycle we see in people who are stressed or anxious: cortisol frees up sugar which, if it isn't burnt off, gets converted to fatty acids and laid down as fat."

Scientists from Brazil and Sweden write: "The production of goods and provision of services 24 hours a day, seven days a week, have risen dramatically over the last decade."

This means more people are working nights, generally with negative consequences for their weight and health.

"Over 50% of the total energy consumed by shift or night workers is consumed during the evening or night. Both the quality and quantity of foods consumed might be influenced by shift or night work and traditional meals at home discontinued."

In other words: when you work nights, you tend to eat unhealthily and mainly eat at night. This is bad for your health, but also tends to make you put on weight because your body can't digest food as efficiently at night as during the day.

If you do work nights, try regular small snacks which are high in protein or fibre: some grilled meat or fish, a salad and plenty of water can help get you through your shift.

You're skipping meals or 'yo-yo' dieting

You're going out for dinner with friends later, so what do you do for lunch? Skip it? This technique is unlikely to lead to weight loss.

"Skipping meals puts your body into self-defence mode: low food intake slows your metabolism down", explains Walford. "So then when you go back to eating normally you're putting food into your body but not burning it off as quickly as before. You end up putting the weight back on and sometimes put even more on than before."

Of course, Walford's talking about the unhealthy technique of skipping meals followed by binge-eating, rather than 'intermittent fasting' (made famous by the 5:2 diet) for weight loss. Intermittent fasting certainly works for some people and the evidence is out there to back it up. But it's a tougher regime for most people to maintain than merely eating a bit less. And it's not a good idea if you've suffered from an eating disorder in the past.

You're into the coffee shop culture

Do you remember when coffee meant instant granules with hot water? Now everywhere you go there's a million choices. These coffees or hot chocolates may taste nice and make you feel good (for a bit) but they aren't a great choice if you're trying to lose weight.

Walford suggests you watch the milk: "Many white coffees or hot chocolates from cafes have much more milk in than you would put in yourself at home."

And of course, coffee shop 'mixed drinks' like a mocha or blended ice-coffee tend to have a lot of sugar in too. Trying to lose weight, but love your coffee? Try black, no sugar.

You're eating more than you think

Studies that go back to the 1990s have consistently shown that we underestimate how much we eat. Believe it or not, twenty years ago scientists wrote: "Individual underestimates of 50% are not uncommon." And more recently investigators from the Czech Republic who looked at a number of studies found about a third of us eat more than we think (by an average of 15%).

If you're having trouble keeping track of what you eat, try snapping a photo of literally everything you eat or drink over a 24-hour period: the results might surprise you.