Do diets deliver?
In this post we’re looking at dieting and weight loss. But let’s be clear, there is more than one definition of the word diet. According to the Oxford Dictionary it can also mean ‘the kinds of food that a person habitually eats’ as well as ‘a special course of food to which a person is restricted … to control weight’. So diet, diets, dieting have become synonymous with restriction and by association denial. Unsurprisingly, embarking on a weight loss plan may look far from appealing.
Weight loss diets have been in existence for decades. Evidence of a low carbohydrate diet was recorded as far back as 1864 by William Banting1. He had been advised to treat his ‘corpulence’ by abstaining from some of the mainstays of his daily diet, for example ‘bread, butter, milk, sugar, beer and potatoes’ and replace them with a diet that consisted mainly of meat, fish, vegetables and fruit. He records being quite incredulous that he would lose weight on such lavish foodstuffs.
But fast forward over 150 years and dieters are still struggling to achieve long-term weight loss. The World Health Organisation report that worldwide incidence of obesity has nearly tripled since 1975 and in 2016 39% of adults were overweight2.
What makes dieting difficult?
The body is well-equipped to manage a reduced intake of nutrients; or even a total lack of nutrition for a period of time.
In the short term, for example during exercise or the early stages of caloric restriction, energy needs are met by glycogen (a polysaccharide formed from branched chains of glucose molecules) stored in the liver and also skeletal muscle. Glycogen acts as a buffer to maintain the level of glucose in the blood. This is especially important for the brain, since glucose is almost exclusively the only energy substrate which brain cells can utilise.
Glycogen reserves in the liver weigh about 100g and in skeletal muscle about 200g. Since glycogen is stored with approximately 3 times its own weight in water, depletion will result in weight loss of over 1kg in the first few hours or days of a diet3. Subsequent weight loss will be less dramatic as fat stored in adipose tissue (fat cells) is then used to complement a reduced energy intake. Psychological aspects and discouragement may then come into play. If unrestricted eating resumes, the glycogen stores and associated water are quickly replenished and the weight regained.
Metabolic adaptation
An item of research carried out in 2013 questioned whether the public health message, often based on the simple energy balance model of less energy in and/or more energy out, was in line with the science4. The study reviewed public health interventions and research trials for weight loss published in 2011. Results pointed to complex feedback machinery within the human body protecting it from weight loss as opposed to preventing fat accumulation. One of these mechanisms which comes into play during periods of caloric restriction is the reduction of the basal metabolic rate* which means less energy is expended when the body is ‘ticking over’.
*Basal metabolic rate (BMR) refers to the basic energy requirements for staying alive, both at the cellular and whole body level. BMR is the largest component of energy expenditure over a 24 hour period, probably in the region of 60%. The remainder is energy used for physical activity and energy used to digest food3.
The phenomenon of the body protecting itself against weight loss is well illustrated in a 2016 study5 which observed 16 severely obese contestants in the TV weight loss show, The Biggest Loser. Having lost vast amounts of weight during the 30 week programme through a rigorous diet regime and intensive exercise, 14 of the original 16 recruits were followed up at the end of the competition and again 6 years later. As well as regaining a significant amount of weight after 6 years, the research team found that for all subjects BMR was suppressed at the end of the competition and remained so after a further 6 years, in the region of 500 kcal per day. This confirmed expectations that in the long term, metabolic adaptation will act to counter a continued effort to lose weight. Given that BMR is relative to body mass, the fact that it remained suppressed despite significant weight gain is key, making further weight loss increasingly difficult.
diabetes.co.uk provide a BMR calculator here, based on gender, age, height and weight
One-size doesn’t fit all
In 2019, a group from Kings College London announced findings from a large study conducted both in the UK and the US – details linked here. Despite many of the participants being twins, including identical twins, different biological responses (blood levels of triglycerides, insulin and glucose) were seen when the subjects consumed the same meals. Since identical twins carry the same genes and results for sets of identical twins were not always the same, this implies that the varied responses could not always be attributed to genetic differences. The timings of meals, the gut microbiome, exercise and sleep were other areas where data was collected during the study. Further analysis of the large volumes of data may suggest that these other factors have just as much bearing on food metabolism as the constituents of the food itself.
Is personalised nutrition the answer?
A 2016 review6 in the Journal of Nutrition cites that a combination of nutrigenomics*, epigenomics** and metagenomics*** may progress to a realisation of personalised nutrition programmes.
*the study of the interaction of nutrition and genes
**the study of the long-term modification of one or more genes by an external trigger, where the DNA code itself is not altered
***here referring to the study of microbial communities, i.e. the gut microbiome
These are all relatively new scientific fields and further investigation is required to understand what level of involvement each has in the management of body weight.
There are success stories
In a collaborative effort from researchers at Brown University and The University of Colorado, The National Weight Control Registry was set up in USA in 1994 – website linked here. This is part of a longitudinal prospective study – results are compared over a future time period – looking at long-term success in weight loss. Tracking and examining the characteristics which have helped individuals lose weight, the study reports that their respondents (80% are female, 20% are male) ‘have lost an average of 66lbs and kept it off for 5.5 years’.
Some commonalities of the study participants include the following:
- 98% modified food intake to lose weight
- 94% increased physical activity – the most frequently reported type of exercise is walking
- 90% exercise on average 1 hour per day
- 78% eat breakfast every day
- 75% weigh themselves at least once every week
On a note of caution, it would seem that much of the data is self-reported; being 80% female the cohort is not representative of the US population as a whole; according to this critique the success rate as a percentage of US dieters is only 0.001%. Wherever there is a yin there is a yang.
References
- BANTING, W. Letter on Corpulence, Addressed to the Public. 3rd ed. London: Harrison, 1864
- WORLD HEALTH ORGANISATION. Obesity and Overweight. Fact Sheet. Updated 1 April 2020. [viewed 28 April 2021]. Available from: https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight
- FRAYN, Keith N. Metabolic Regulation: A Human Perspective. 3rd ed. Chichester: Wiley-Blackwell, 2010
- HAFEKOST, K. et al. Tackling overweight and obesity: does the public health message match the science? BMC Medicine [Online]. BioMed Central. 18 February 2013, 11 (41). [viewed 28 April 2021]. Available from: 10.1186/1741-7015-11-41
- FOTHERGILL, E. et al. Persistent metabolic adaptation 6 years after The Biggest Loser competition. Obesity (Silver Spring). [Online]. August 2016, 24(8). 1612-1619. PMC. [viewed 29 April 2021]. Available from: doi: 10.1002/oby.21538
- GONI, L. et al. Future Perspectives of Personalised Weight Loss Interventions Based on Nutrigenetic, Epigenetic and Metagenomic Data. The Journal of Nutrition. [Online]. April 2016, 146(4). 905S-912S. Oxford Academic. [viewed 29 April 2021]. Available from: doi: 10.3945/jn.115.218354
