With almost half the adult population trying to lose weight - it’s time to bust some diet myths that just won’t go away.
Here’s eight we’ve been asked about lately.
1. Celery has “negative” calories
A 15cm (five calories). Your body uses about 10 per cent of the celery’s total kilojoule value to digest it. This is .
In practical terms it’s just one or two . The only thing with “negative calories” is cold water.
That’s because it needs to warm up to body temperature before it can be absorbed. That “heating” uses up some kilojoules. Water itself contains no kilojoules, so the overall effect is “negative”.
A celery stalk has 19 kilojoules. Source: Gallery
2. Not eating after 7.00pm speeds up weight loss
More important than the time of day you eat, is what you eat and how much you eat.
Your total kilojoule intake, plus the physical activity performed over a whole day determines whether you gain, lose, or maintain weight.
No matter when you eat, if you take in more kilojoules than you need, your body will store the excess as fat.
A recent , where you eat your whole days food as either one, two or three meals per day, makes almost no difference to body weight.
No matter when you eat, if you take in more kilojoules than you need, your body will store the excess as fat.
Some short term studies have found that eating MOST of your kilojoules late in the day could make blood sugar control worse, but longer term trials are needed to check this.
An advantage of closing down the kitchen early is that less total food gets eaten, especially less junk food and less alcohol.
3. Drinking water before meals makes you lose more weight
This one could work for some. A recent randomised controlled trial assigned half to drink 500ml of plain water 30 mins before breakfast, lunch and dinner, while the other half had to visualise their stomach being full 30 minutes before meals.
A comprehensive review of randomised controlled trials on the effects drinking more water on energy intake and metabolism found highly variable results that ranged from negative, to null, to positive effects.
Both groups lost weight over 12 weeks, but those in the water drinking group lost 1.3 kg more than the visualisation group.
A on the effects drinking more water on energy intake and metabolism found highly variable results that ranged from negative, to null, to positive effects. But drinking plain water can help to reduce total daily kilojoule intake when it replaces drinks like softdrink, cordial and juice.
Drinking plain water can help to reduce total daily kilojoule intake when it replaces drinks like softdrink, cordial and juice. Source: Flickr/Enid Martindale
4. Ketogenic diets are better than other diets
Ketogenic diets drastically cut carbohydrate and are very high in fat and protein. A that ran for at least one year, found slightly greater weight loss of 900 grams in those following a ketogenic diet compared to a low-fat diet.
Another examined the impact of two types of severely on appetite.
These diets are very restrictive and should only be used under medical supervision due to potential side-effects.
Meta-analyses of the two ketogenic diet studies that severely restricted carbohydrate found they reduced hunger and lowered desire to eat. The three very low energy diet (VLED) studies, where total energy is restricted to under 2,500 kilojoules per day, found significantly lower hunger levels, with greater fullness and satiety. These diets are very restrictive and should only be used under medical supervision , including headaches, bad breath, gall bladder disease and constipation.
5. Chewing gum speeds up weight loss
Chewing sends signals to your brain that you’re starting to eat and will soon feel full. tested whether chewing hard or soft gum, or none at all, affected appetite.
They found chewing any gum led to a small decrease in energy intake in lean adults, but tended to increase food intake in those who were overweight. A evaluated evidence on relationships between chewing, appetite and food intake.
Chewing gum can make some people feel less hungry, but can have the opposite effect in others. Source: Flickr/Colin Alexander
found chewing was associated with reduced feelings of hunger, while 10 of 16 experimental studies found chewing reduced food intake. They noted a publication bias existed, meaning studies with positive findings were more likely to be published. Interestingly, the impact of chewing gum as part of a weight loss intervention hasn’t been tested.
6. Don’t eat before a workout to burn more fat
Should you eat before a work out? Debate rages, but this has been tested in total energy expenditure and amounts of fat and carbohydrate burned up before, during and after exercise in 12 active healthy males.
They were tested following an overnight fast and on another day after eating breakfast. Fasting before exercise gave a 15 per cent greater rate of fat burning during exercise, compared to eating breakfast. However, eating breakfast led to a 20 per cent greater total exercise energy expenditure compared to fasting.
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7. Green tea speeds up metabolism
A of 15 studies in adults with overweight or obesity examined the impact of green tea on weight loss and weight maintenance and found no significant long-term effects.
But a recent on the effects of any type of tea or tea extracts found small beneficial effects on weight loss, but the results need to be interpreted with caution due to the poor quality of some included studies.
A recent review in adults with metabolic syndrome on the effects of any type of tea or tea extracts found small beneficial effects on weight loss. Source: Getty
8. Eating grapefruit melts fat
No need to rush out in search of grapefruit.
A meta-analysis of three randomised controlled trials on the effect of found no change in body weight compared to controls.
, Professor in Nutrition and Dietetics, ; , Postdoctoral research fellow, ; , Postdoctoral Research Fellow, Nutrition & Dietetics, ; , Postdoctoral Researcher, , and , Associate Professor Nutrition and Dietetics, .
Disclaimer: Clare Collins is affiliated with the Priority Research Centre for Physical Activity and Nutrition, the University of Newcastle, NSW. She is an NHMRC Senior Research fellow. She has received a range of research grants including NHMRC, ARC, Hunter Medical Research Institute, Meat and Livestock Australia, Diabetes Australia, the Heart Foundation. She has consulted to SHINE Australia, Novo Nordisk, Quality Bakers and the Sax Institute. She is a spokesperson for the Dietitians Association of Australia on some specific nutrition issues, including Australia's Healthy Weight Week.
Megan Rollo has received research funding from a number of bodies including Diabetes Australia, Hunter Medical Research Institute, New South Wales Government (TechVoucher) and Novo Nordisk, and consulted to the Sax Institute and Quality Bakers Australia Pty Limited. She is affiliated with the Priority Research Centre in Physical Activity and Nutrition at the University of Newcastle and a member of professional organisations including the Dietitians Association of Australia.
The Diet Testers, a new documentary series hosted by Dr Xand van Tulleken and dietician Hala El-Shafie, in which members of the public road test the most hyped up and written about diets on the market today. Airs from Thursday 1 March at 8.30pm then on
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