Why Diets DON'T work
I touched on this a bit in my post about recent anti-obesity public health campaigns (see it here), but I want to give you a more in depth explanation about why diets do not work.
The diet/weight loss industry is a multi-billion dollar industry ($158.2 billion in 2015), and has been for many years now. There are countless books, shakes, bars, groups, pieces of equipment on sale worldwide- and we buy into it! Over 70% of Brits say that they are on a diet most of the time. Given that rates of overweight and obesity are around 60% in the UK, dieting as a method of preventing/reversing obesity doesn’t seem to be working.
Here’s the thing- diets do generally result in weight loss, however only in the short term.
What happens when you diet:
Start diet- probably involves restriction of food (types or amounts or both).
Cravings kick in because the body is deprived of calories (and sometimes nutrients)- we most often crave sugar and carbs when we are deprived because they provide easily accessible energy.
We stick with the diet through the cravings and eventually they stop- our body has adjusted to a reduced energy level by optimising its processes. Our bodies are great at adapting- think back to when we had to hunt/gather/move around to find food. Sometimes we had to wait days for food, so we learned to cope. They body does things using less energy, and also conserves more energy when it gets some.
We stop the diet and return to normal eating (or binge)- and our clever body thinks “hey loads of extra calories, better save these for later!”. So that’s what it does. As we are already running more efficiently (i.e. using less calories than before), the extra calories are not needed and we decide to store them in case we don’t get extra again for a while.
We continue eating as normal (before dieting)- and ultimately gain weight, usually more than we initially weighed. Because our metabolism has slowed down to accommodate fewer calories, more is stored as adipose tissue (fat).
Subsequent dieting/weight loss attempts will be more difficult- there will be more weight to lose than the last attempt and our metabolism slows down more and more with each attempt.
This probably sounds familiar to a lot of you. Try a diet, lose some weight, stop the diet, gain weight, find another diet…This is called weight cycling (or yo-yo dieting), because weight fluctuates regularly.
Weight cycling is not healthy. In fact, it has many adverse effects on health:
Weight loss attempts can lead to future weight gain. A study of 3536 men and 4193 women (followed for 6-15 years) found weight gain was positively associated with weight loss attempts or dieting behaviour. (Korkeila et al. 1999).
Weight cycling can result in higher blood pressure. 192 obese women were tested- 96 were weight cyclers and 96 were non-weight cyclers. Blood pressure was significantly higher among those who weight cycled. High blood pressure is a risk factor for cardiovascular events (like heart attacks and strokes) and cardiovascular disease, as well as kidney disease. (Guagnano et al. 1999)
Dieters are at a greater risk of low bone mass (and therefore subsequent osteoporosis). A study of obese, restrained eaters (dieters) aged 30-45 found that 31% had osteopenia or osteoporosis. They found a significant negative association between bone mineral content and number of times a weight loss diet was undertaken- i.e. the more diets, the lower the bone mineral content. They also found a significant positive association between bone mineral content and energy expenditure (physical activity)- i.e. the more active, the greater the bone mineral content. (Bacon et al. 2004)
If you are thinking “but diets must work, I’ve been told to go on…” or “ but Mary down the road did…and lost a pile of weight”…diets can work for some people, but not long term. Intervention studies looking at different diets don’t even prove that diets are effective (and people taking part generally have a lot of support!). Weight loss studies are often reported in the media as successful, but if you actually look into the data, there are lots of problems.
Studies on weight loss interventions are prone to several key problems:
Excessive access to the research team (generally including a nutritionist or dietitian) - some studies reported participants meeting researchers 10 times in a six-month period. This is very unlikely to occur in the general population.
Participants are offered incentives- people who take part in studies sometimes receive money, get food or meals for free, have free access to healthcare professionals, get gym access and more. Again not likely to happen at population level.
Small sample sizes and a high dropout rate- considering the potential benefits for participants, these intervention studies see a large amount of individuals leave before the study has ended. It is estimated only 33% return at the end of studies. Small sample sizes make it difficult to generalise the results to the population.
They are carried out for short (and varying) lengths of time. Many dietary interventions run for less than a year, although dieting/restrained eating would have to be constant to maintain weight loss. Therefore, we can only say diets work in the short term- many studies have yet to find out what happens over longer periods, although studies with decent follow up periods consistently show weight regain. Additionally, as intervention lengths vary it is really hard to compare different diets- we can’t compare an intervention that lasted 2 weeks with one that lasted 9 months.
The follow up time varies too- that is the time after an intervention has ended that the researchers check in with participants. Usually in intervention studies data will be collected at baseline or before the research starts, at multiple times throughout the intervention, at the end of the intervention and a while after the intervention has ended (or sometimes a few times after the end). Some studies only follow up a week or two after the intervention, while others follow up for a few months. Again, this makes it difficult to compare different studies- varied follow up times make it difficult to compare rates of weight regain.
Some studies don’t present follow up data as part of their main research- this really upsets me. Certain researchers have followed up with participants and when weight regain was noted, failed to present that information in their published research (but you could PAY EXTRA to view full data, which showed not only weight regain, but showed participants weighed more after follow up than prior to the intervention!!).
What often happens is that there is significant initial weight loss (e.g. in the first 6 months) reported. Weight at the end of the intervention (e.g. 1 year) is still lower and therefore deemed to indicate success. However, if you look at the data, weight has increased between 6 months and a year- indicating weight regain has begun. In studies where this occurs, there is almost NEVER provision of follow-up data, because it will show that participants regained all the weight they lost in the initial phase!
Don’t believe me? Here are some weight loss intervention studies and their results:
Howard et al. 2004 tested a low-fat diet or control (general healthy eating advice) on 48,835 post-menopausal women in the USA. The authors reported that the diet resulted in weight loss, but a look at the data shows an average loss after 1 year of 1.9kg and after 7 years of 0.4kg- not exactly the answer to obesity..What’s more is both groups remained in the same BMI throughout- at follow-up both groups remained at BMI 29, the intervention group average BMI was 29.0, while the control group average was 29.2.
Gardner et al. 2018 pitted the low fat diet against the low carbohydrate diet. They reported similar weight loss for both groups at 12 months. They concluded that both diets work and should be chosen based on personal preference. However, they didn’t provide any follow-up data- unless you paid for it. Luckily, someone I follow got the supplementary data and shared it. The follow-up data shows that mean weight after follow-up did not indicate significant weight loss, but instead indicated weight regain, with many participants weighing more at follow-up than baseline.
Haggerty at el. 2017 trialled a telemedicine weight loss intervention on 196 obese participants (survivors of endometrial cancer). The intervention lasted 6 months and reported no follow up. Participants received telemedicine with either wi-fi scales, texting or enhanced usual care. All intervention groups lost weight, however weight loss was non-significant (i.e. they didn’t lose very much) (averages were 3kg for wi-fi, 4.4kg for texting and 1.8kg for usual care). Although we do not know what happens to weight after 6 months (and when the intervention is finished) and although the weight lost was not a significant amount, the authors conclude that interventions such as these are successful at producing weight loss.
A comprehensive review (Mann et al. 2007) found that one to two thirds of dieters regain MORE weight than they lost on their diets, stating that “studies likely underestimate the extent to which dieting is counterproductive because of several methodological problems, all of which bias the studies toward showing successful weight loss maintenance”. The review also say that “studies do not provide consistent evidence that dieting results in significant health improvements, regardless of weight change. In sum, there is little support for the notion that diets lead to lasting weight loss or health benefits”.
As you can see, the evidence behind diets is virtually non-existent! The evidence instead tells us that diets don’t work, and in fact long-term dieting can be bad for our health.
What are your thoughts on dieting?! Drop me a comment or a DM and let me know.
Lots of love,
Little O x