Do you watch what you eat and exercise but can't seem to lose weight, no matter how hard you try?
What's making you fat?
Dr Shahrad Taheri, explains: "We discovered that people who sleep for significantly less than seven hours a night often end up being obese.
"Lack of sleep seems to stimulate the hormones that regulate appetite. It leads to higher levels of ghrelin, a hormone that triggers appetite, and lower levels of leptin, that tells your body it's full."
Time for an early night we think!
David Cameron-Smith, explains: "When we're stressed, our adrenal glands release a hormone called cortisol, which makes us store fat in case of famine.
"This fat gain can become concentrated in our most active fat cells around the abdomen, which are highly sensitive to stress hormone receptors."
The good news is that exercise will help beat stress, improve your mood and burn fat.
"Women on average gain just under two kilos," says Valerie Burke, research fellow from the university's School of Medicine and Pharmacology.
"In part, this is because couples tend to cook more gourmet-style meals and women start serving themselves portions that are as large as their partner's."
Why not take up a sport you can do together? Or go for a long walk hand-in-hand every Sunday.
They claim the adenovirus attacks tissue and causes fat cells to multiply, leading to massive weight gain, regardless of food consumption.
Their tests found that almost a third of obese adults carry the virus, compared with 11 per cent of slender men and women.
So does that mean we should avoid obese people in the street? According to professor Nikhil Dhurandhar that would be pointless: "People could be fat for reasons other than viral infections, so it's really pointless to try to avoid fat people to avoid infection."
As well as having significant impact on our aerobic fitness, our genetic makeup also affects our ability to burn fat through exercise.
The study followed 500 volunteers who undertook cardiovascular exercise were for 30 minutes, five times a week. By studying the volunteers' DNA they found 30 genes that affect oxygen uptake during aerobic exercise, such as cycling.
Approximately 20 per cent of the volunteers had a genetic makeup which meant their oxygen uptake hardly changed, despite weeks of exercise.
Although scientists have yet to devise a gene test for obesity, we do know that there's an 80 per cent chance you'll be overweight if both your parents are obese.
If one of your parents is obese there is a 40 per cent chance you will also be overweight.
However, if neither of your parents are obese, you have just a 10 per cent chance of developing a weight problem.
Your body could be struggling to metabolise a food it is sensitive to, causing weight gain and fluid retention.
Wheat and dairy products are the most common culprits.
However, cases are still relatively low - only two people in 100 of the UK population.
If you think you may have a food intolerance, visit your nutritionist or GP, who can perform a blood test.
Remember to seek professional advice before eliminating food groups from your diet.
It can cause infertility, and symptoms include obesity, hair loss, excessive hair growth, acne and irregular periods.
The condition affects between five and 10 per cent of all women of childbearing age, regardless of race or nationality.
If you are concerned, see your GP, who will run an ultrasound test to check for polycystic ovaries.
See your GP if you suffer from cold hands, fatigue, depression, coarse dry hair, constipation or irritability - as these are all symptoms of hypothyroidism.
Located just under the Adam's apple in the throat, the thyroid gland secretes hormones into the bloodstream that control the body's metabolism, which is why problems with the gland can lead to weight gain.
Medication, or in some cases, surgery can be the answer.
Steroids, prescribed for asthma, lupus, arthritis and inflammatory bowel disease, are the worst offenders.
Anti-depressants, the contraceptive pill, HRT and drugs for type II diabetes can also cause weight gain.
Consult your GP about alternatives if you are worried Remember, never stop taking prescribed medicines without talking to your doctor first.