Christmas is a distant memory. For some of us, the annual mission undertaken by chocolate, mince pies, brandy butter and yule log to convert themselves into excess body fat has been a success. Once again we find ourselves in post-yuletide gloom, with weight to lose and fitness to gain.
We all know that New Year resolutions are made to be broken. As the fireworks break out and we blow up what is definitely our last supersized bag of crisps of the season with a salty bang, it’s all too easy to go online and sign up to membership of the local gym. It’s also not that difficult to declare that alcohol will not touch our lips for the foreseeable future and filling up our supermarket trolleys with healthy stuff, including items disregarded in the approach to Christmas (and possibly at most other times of the year too), such as celery and low fat cottage cheese, requires little in the way of moral fibre when we’re still feeling bloated and slightly nauseous due to our recent excesses.
Most of us have learnt, though, that a few days later, plunged into January darkness, when we’ve gone back to work and the Christmas decorations have come down, all this resolve evaporates. The local minimarket, which is open until midnight, sells chocolate, and surely the occasional beer won’t hurt as long as we make sure we eat a bit of salad every now and then?
But what about serious dieters – those that really mean it? What are they getting into when they embark on a weight loss regime? Do they lose weight in the short term and can they prevent themselves from re-gaining the weight later? Also, how does dieting affect their overall health and metabolism?
Popular weight loss diets
It’s clear that many of the wide range of slimming diets available would lead to fairly rapid weight loss if it was possible to stick to them, simply because they involve a drastic reduction in calorie intake. There’s, to name a few:
- The raw food diet
- The Atkins diet
- The Dukan diet
- The cabbage soup diet
- The grapefruit diet
- The baby food diet
- The paleo diet
- The purple diet (only purple foods are allowed)
- The hallelujah diet (only includes foods mentioned in the Bible)
- The urine therapy diet (don’t ask)
- The VB6 (vegan before 6 pm, then anything you fancy) diet
- The sugar-free diet (excludes all sources of sugar, including healthy ones, such as fruit)
- The clay cleanse diet and the lemonade diet, endorsed by Beyoncé, which involves a terrifying-sounding and surely rather reckless “salt water flush”.
These diets seem to me to be pretty easy to invent. I’ve just come up with one of my own – the Malteser diet – all you have to do is eat five Maltesers at breakfast, lunch and dinner for a week (and nothing else, obviously). If this seems a little harsh, you could up it to ten Maltesers per meal at weekends for a treat. As each Malteser contains less than eleven calories, any excess body fat would soon melt away.
Clearly, the Malteser diet and some of the others mentioned above are not healthy, long term options. The only reason people on them don’t suffer from malnutrition is because they use them on a planned short term basis or they can’t keep to them and gain most of their nutrients from the cheese and pickle sandwich they cheat with when they’ve fallen off their particular diet wagon.
Luckily, more reasonable or mainstream options exist, including the points based system offered by Weight Watchers and the 12 week weight loss plan recommended by the UK National Health Service (NHS). However, these are longer term propositions. They can’t promise a drop in jeans size in a week, but require staying power and patience. In my experience, you really have to stick to these diets to lose weight – they aren’t as low in calories as some of the more extreme diets, so if you stray beyond their limits it won’t take many biscuits or chocolate bars to put you up into realms of normal non-weight-reducing calorie intake.
There’s also the 5:2 diet, which I tried for a while: knowing that I could eat normally on five out of seven days helped me to stick to it over several months, and I did lose weight, but on the two fasting days my reduced blood sugar levels turned me into a dangerous maniac at about four in the afternoon…
Health impact of weight loss diets
Assuming you stick to a particular diet for long enough to lose weight, and excluding some of the wackier options, what sort of health effects can you expect?
A BMI of 25 to 25.9 makes you overweight, whereas a BMI of 30 to 39.9 makes you obese and a BMI greater than 40 puts you into the severely obese category. Some people with a high muscle mass and little or no excess fat could be defined as obese according to BMI, so waist circumference may be a better indicator of excess fat; values higher than 94cm (37in) for men and 80cm (31.5in) for women are likely to lead to obesity-related health problems.
Obesity is a condition associated with inflammation of adipose tissue. It can lead to increased risk of a number of conditions, including diabetes, metabolic syndrome, coronary heart disease and certain types of cancer, so it’s clear that apart from the obvious advantages of weight loss, such as being able to wear a bikini on the beach, there are health benefits.
Many studies bear this out. For example the functions of natural killer cells, the first defence of the body against malignant cells, are considerably impaired in obesity, but their functionality can be reactivated by fat mass reduction. Another study showed that reductions in adiposity led to increases in circulating 25-hydroxyvitamin D levels.
Do different types of diet lead to different health outcomes?
High protein diets
High protein diets, often accompanied by low carbohydrate intake, as in the Dukan diet, are popular and have been shown to be effective. In one study, children who consumed high protein breakfasts demonstrated greater post-prandial energy expenditure and fat oxidation, together with reduced hunger, compared to those consuming carbohydrate-based breakfasts.
High protein intake has also been linked to reduced BMI and waist circumference, as well as increased circulating levels of HDL cholesterol, indicating lower risk of cardiovascular disease. In another study, a diet relatively high in protein, accompanied by low glycaemic index carbohydrates and omega-3 PUFA led to both successful weight loss and a reduction in systemic inflammation. However, research on mice suggested that high protein intake can lead to undesirable proatherogenic changes.
Low carbohydrate diets
The ketogenic diet is a low carbohydrate diet accompanied by relatively high fat and moderate to adequate protein intake. It has therapeutic applications, for example in the treatment of epilepsy in children. However, it also features in several weight loss plans, the theory being that the diet forces the body to burn fats rather than carbohydrates.
The initial stage of the Atkins diet, for example, is ketogenic. During this phase, participants can eat meat, eggs, cheese, olive oil and butter, but their only sources of carbohydrates are salad greens and non-starchy vegetables, an approach that has been shown to result in significant weight loss. However, it has been claimed that much of this initial decrease in body weight is caused by water loss.
Evidence exists to support the contention that ketogenic diets lead to appetite suppression, which is obviously helpful during attempts to lose weight. Concerns have been expressed, however, that the Atkins or New Atkins diet (which allows a wider variety of foods) could increase risk of heart disease, and some nutritionists are unhappy about the fact that the diet encourages its users to increase their salt intake. Another study found that variations in the carbohydrate and glycaemic index of the diet had little impact on fat mass reduction.
This increasingly popular approach to weight loss, involves severe restriction of energy intake. In the 5:2 diet, this occurs for 2 days per week, with completely unrestricted eating on the other 5 days. Alternate day fasting is another option. The success of this diet hinges on the unrestricted eating component. If energy intake on non-fasting days is high enough to compensate for the limited intake on the fasting days, it won’t work.
This diet model has been shown to be an effective means of losing weight, but its impact on other health outcomes is, as yet, uncertain. However, several older studies suggest that it prolongs life in rats and one more recent study showed that alternate day fasting led to anti-inflammatory effects in mice. Another study indicated that time-restricted feeding improved some of the risk factors associated with metabolic disease.
All over the world, people discover food research with FSTA. Find out more.
How many people really lose weight when they go on a diet?
Is it really feasible to expect weight loss diets to work, particularly in the long term? As shown above, many diets do lead to weight loss and improvements to various metabolic parameters if they are adhered to. However, sticking to a diet regime isn’t as easy as it sounds and keeping the weight off afterwards can be extremely difficult. Relapse rates are high and are often simply due to the temptation offered by readily available, palatable food.
One study revealed evidence of behavioural compensation, in which even highly compliant participants undertaking dietary restriction or exercise programmes achieved 12–44% and 55–64% less weight loss, respectively, than expected. This was due to the fact that they compensated for the negative energy balance aimed at in the intervention by increasing their energy intake or reducing their energy expenditure.
In an investigation revealing factors influencing drop-out rates from weight loss programmes, only 33.1% of participants were deemed to be successful, achieving more than 5% weight loss after 1 year. Initial weight loss after 1 month was positively associated with long term success, whereas being married was a negative predictor.
Previously overweight or obese people tend to regain weight after dieting. In a group of patients treated for weight loss by primary care physicians, weight loss maintenance (defined as maintenance of an initial weight loss by patients with a BMI greater than 25 kg/m2 of 10% for more than a year) was achieved by only 26.7% of the group. 25.7% failed to maintain the weight loss and 47.6% (known ignominiously as the “failure group”) didn’t even achieve the weight loss in the first place.
Metabolic adaptation to weight loss
The previous study shows that weight loss is difficult. But it shows something else too: weight control after dieting is difficult. One of the reasons for this is metabolic adaptation to the reduced calorie intake. Resting energy expenditure is reduced via adaptive thermogenesis, a situation that both slows down weight loss during the dieting phase and promotes weight regain during the post-diet phase.
The 5:2 diet may avoid this metabolic adaptation because fasting never takes place for more than a day at a time, and is followed by one or more days of normal eating. It has also been suggested that each individual’s body has a set-point, a pre-set weight that may be higher than that achieved by dieting, leading them to eat more to regain that lost weight.
But there is some hope because certain types of diet may help to minimise these effects. For example, in a recent weight maintenance trial, macronutrient content of the diet was found to be an important factor, with higher protein intakes leading to reduced weight regain. In addition, a review of 14 trials found that weight loss was more sustainable if Mediterranean, vegetarian and low fat dietary patterns were observed.
The problem of yo-yo dieting
Also known as weight cycling, this is defined as the repeated loss and regaining of ten pounds or more over a five-year period. It is often associated with extreme diet regimes, which are ultimately impossible to maintain. Some health experts have suggested that yo-yo dieting actually causes weight gain in the long term, and that because the extreme dieting can trigger the body’s starvation response, which leads to rapid weight gain of only fat during the non-diet phase, yo-yo dieters end up with a reduced muscle to fat ratio.
Many websites state categorically that yo-yo dieting can lead to a range of adverse health effects, including cardiovascular problems and cancer. However, one review of the literature found little evidence that weight cycling affected risk of morbidity or mortality. Similarly, a recent study involving a large cohort in the US, found no associations between yo-yo dieting and risk of any of the individual cancers investigated.
Perhaps the worst impact of yo-yo dieting or any weight regain after dieting is psychological – it’s extremely disheartening to make the huge effort needed to lose weight, only to put it all back on again afterwards.
Metabolically healthy obesity
A subset of obese patients exists that doesn’t demonstrate the cardiovascular and metabolic risk factors traditionally associated with obesity – they are known as the metabolically healthy obese (MHO). At the same time, a group of normal weight patients has been identified that do carry the risks connected to obesity – metabolically unhealthy normal weight patients.
There is some uncertainty about the diagnostic parameters used to categorise patients into these two groups and estimates of the numbers of individuals involved vary, but one study suggested that prevalence rates of MHO ranged from 2% to 75%; another study found a prevalence of 57% among overweight adults, when classified by visceral to subcutaneous fat ratio, and research coming out of Korea indicated that 47.7% of obese individuals were MHO.
If a person is obese or overweight, is there anything they can do to improve their metabolic profile and increase their chances of being MHO?
Genetic factors may make a contribution and research into these is ongoing. Nevertheless, one study found that MHO adolescents and women aged 19–44 ate healthier diets than their metabolically unhealthy counterparts, although no significant differences were observed for males aged 19–44 or in adults of both sexes aged 45–85.
Another study found that MHO participants exhibited superior dietary quality and closer compliance with food pyramid recommendations, as well as both moderate and high levels of physical activity. Interestingly, this study also found that MHO prevalence was higher in females and tended to increase with age.
Gene expression and metabolic profile can be influenced by diet, as shown in a study in which obese and diabetic mice given diets containing docosahexaenoic acid exhibited beneficial alterations in expression of endocannabinoid and inflammatory genes, as well as improvements in metabolic parameters associated with glucose use in muscles.
So, is dieting worth the effort?
In essence, yes – it can be. There is no doubt that sustainable weight loss can improve health. Also, some researchers feel that it’s only a matter of time before even the MHO develop the metabolic dysfunctions typically associated with obesity, a prognosis that could obviously be attenuated by losing a bit of weight.
But for most of us, dieting really doesn’t work. It’s an uphill struggle both to lose weight and to keep it off – even our own metabolism is against us! I can’t help feeling that much of the scientific research on the health benefits of weight loss and many of the diets peddled by “experts” offer false promise by focusing on the short term benefits and ignoring the key fact that most people regain the lost weight afterwards. It’s the ultimate example of the triumph of hope over experience – each time we embark on a new diet, we tell ourselves that this time it will be different, this time it will work.
But let’s not despair. Two studies cited in a recently published review on associations between fatness, fitness and all-cause mortality found that overweight and fit people had better survival that normal weight unfit people.
So, perhaps the best approach is just to eat healthily (most of the time, anyway) and take plenty of exercise. Who knows? We might even lose some weight!
- What are the Superheroes of a Healthy Diet?
- Have High Protein Diets Had Their Day?
- Gluten-Free Diets. Are They a Fad?
At IFIS, we are passionate about food science and news. To receive our monthly Thought for Food blog posts, subscribe below: