If weight loss is simply a matter of eating less and moving more, why do so many people struggle to achieve and maintain a healthy weight?

 

 

Standard advice on how to lose weight has always been to “eat less and move more”. This is based on the assumption that the body is a closed system that obeys the first law of thermodynamics i.e. any change in the energy store (amount of fat) depends on the input (food) and output (metabolism and exercise). In other words: ‘energy store = energy in – energy out’.

From this equation, it follows that if the body consumes more energy than is required, excess energy is stored as fat and the individual gains weight. Conversely, expending more energy than is needed creates a negative energy balance and so weight is lost.

While reducing calorie intake and/or increasing physical activity will lead to reductions in weight, this loss is invariably not sustained over time. A comprehensive review of weight loss trials by Mann et al in 2007 found that the greatest weight loss occurs after six months, with mean losses of 5-8kg, after which it tends to plateau. Another review of studies lasting up to 48 months found that weight losses reduced to 3-6kg.

Nevertheless, a recent study in the American Journal of Preventive Medicine found that a large initial weight loss is associated with better long-term outcomes, with the majority of individuals who had sustained a weight loss of 30 pounds or more for at least one year maintaining it for 10 years.

Fine balance

It is becoming increasingly clear that the level of body fat or energy store is under homeostatic control. The body appears to have a body fat ‘set point’, detects any deviations from this level and adjusts the metabolic rate to maintain this level by either increasing or decreasing energy expenditure.

The ‘control centre’ resides in the brain and research is beginning to discover how it works, how it goes wrong when we become obese and why it puts up a fight when we try to lose weight. A better understanding of this system could go some way to providing a solution to the obesity epidemic.

The co-ordination of body fat stores is located in the hypothalamus, which helps regulate a range of functions, such as body temperature, hunger, circadian rhythms, as well as emotions, learning and memory. The hypothalamus receives input from the gastrointestinal tract on nutrients and the calorie content of food, interprets this information and acts upon it through connections with other areas. The hypothalamus receives information on the levels of body fat from the hormone leptin. If levels fall following weight loss, the hypothalamus increases hunger and reduces energy expenditure. Conversely, higher levels of leptin trigger mechanisms to reduce appetite and increase energy expenditure. However other factors are clearly involved otherwise weight gain would never occur.

Hedonic eating

Food intake is driven by the body’s requirement for energy and this basic biological need is termed ‘homeostatic feeding’. Intake can also be driven by the palatability aspects of food and this is termed ‘non-homeostatic or hedonic feeding’. The palatability of food is related to its flavour and texture – and foods with higher levels of fat are more palatable.

This has not gone unnoticed by the food industry, which modifies the combination of sugar, fat and salt in processed foods to improve our taste experience so that such foods become rewarding (i.e. they generate pleasurable sensations so that we always want more).

Another important factor affecting the amount of food eaten is calorie density, which is a measure of the number of calories per unit weight or volume of food. If the calorie density of a food is increased, it becomes less satiating (i.e. you need to consume more of it to become full). Both palatability and calorie density strongly affect the satiety of a food, such that foods like chocolate, biscuits and cakes are more palatable and calorie dense and less satiating, so that we end up eating more of them.

The facts about fibre

Formerly known as roughage, dietary fibre refers to substances found only in plant foods that cannot be completely broken down by digestive enzymes. These substances include waxes, lignin and polysaccharides such as cellulose and pectin. NHS figures suggest that most Britons fall short of the recommended daily target of 18g, with average intakes at 12-14g per day.

According to the British Nutrition Foundation, a low fibre intake is associated with constipation and some gut diseases, such as bowel cancer, while a high fibre diet may help reduce cholesterol and lower the risk of diabetes. Eating high fibre foods can also aid weight loss by making individuals feel satiated for longer.

Fibre is divided into soluble and insoluble fibre and a healthy diet should contain a combination of both. The former dissolves in water and can be partially fermented in the gut. It slows the digestion of food, helps prevent excess cholesterol from being absorbed and softens stools. Soluble fibre is found in oats, barley, beans and pulses, and certain fruits and vegetables. Insoluble fibre passes through the digestive tract without being broken down, adding bulk to the stools and aiding the digestion of other foods, thereby helping to prevent digestive health problems, such as constipation and haemorrhoids. Good sources include bran, wholemeal bread, wholegrain cereals, and nuts and seeds.

NHS Choices recommends stepping up fibre intake gradually as a sudden increase may result in unpleasant symptoms (e.g. abdominal cramping and bloating). Drinking more fluids, aiming for approximately 2.5 litres a day, may help to ease these symptoms.

Reward pathways

In order to understand how highly palatable foods contribute to obesity, it is necessary to consider a second circuit in the brain called the mesolimbic pathway. This pathway is thought to be involved with the reward system in the brain (i.e. the system that regulates and controls behaviour induced by pleasurable stimuli such as food, water and sex) and uses dopamine as the main neurotransmitter. In the presence of these stimuli, dopamine is released and directs behaviour towards obtaining them.

The mesolimbic system is central to the development of addiction to narcotic and stimulant drugs because these agents cause an increased release of dopamine within the reward system. Evidence is emerging that highly palatable foods (i.e. those with high levels of sugar and fat) can activate the same dopaminergic pathways.

The desirability of highly palatable foods has been shown in animal models using the ‘cafeteria diet’. This diet consists of a range of human junk foods such as biscuits, breakfast cereals, processed meats and peanut butter. Studies show that rodents will endure cold temperatures to be allowed access to the cafeteria diet, even when their normal food is readily available. Studies in humans show that, when given access to junk foods, over- consumption occurs.

In reality, the reward system is more complex and involves other endogenous agents including opioids and cannabinoids, with receptors for both located in the hypothalamus. The role of cannabinoids is unclear but research has revealed that marijuana increases the desirability of highly palatable foods, especially sweet foods. In a study in which people were allowed to smoke marijuana, calorie intake was increased by approximately 40 per cent and the extra calorie intake was due to snacking on sweet foods such as chocolate bars and crisps.

Cannabinoids are clearly involved in regulation of energy balance, as shown by the efficacy of cannabinoid antagonists, such as the anti-obesity drug rimonabant (Acomplia), which was withdrawn in 2008.

Endogenous opioids influence satiety and opioid receptors are found in areas of the brain related to food intake and reward. Work with rodents has found that highly palatable foods delay satiety signals allowing over-consumption – this explains in part why we always find room for something from the dessert trolley even though we feel full after a big meal – and this effect can be blocked by opiate antagonists.

Did you know?

• A large initial weight loss is associated with better long-term outcomes
• Highly palatable foods fuel obesity by acting on the brain’s reward pathways
• High fat diets alter the brain’s responses to the hormone leptin

Hypothalamic inflammation

When first discovered it was believed that exogenous administration of leptin would be an effective cure for obesity because the hypothalamus would sense the higher leptin level and increase energy expenditure, leading to weight loss. However, it soon became clear that obese individuals were hyperleptinaemic and administration failed to reduce weight.

To discover why obese patients are hyperleptinaemic, experiments in rodents were undertaken and these revealed that high fat diets induce the formation of inflammatory mediators within the hypothalamus, which alter the brain’s ability to respond to leptin signalling. Furthermore, blocking these inflammatory mediators reduces obesity and improves the hypothalamic response to leptin.

These observations suggest that, in obesity, inflammatory changes in the hypothalamus prevent the correct interpretation of leptin levels but also that the hypothalamus defends a higher level of leptin more than a lower level. This makes sense from an evolutionary perspective. If leptin levels fall, the brain perceives this as more of a danger to survival (i.e. starvation) than having higher levels, which implies more stored energy.

Pharmacy versus obesity

Obesity levels have continued to rise unchecked in the UK (reports Charlotte Rixon). The latest Government figures show that in England alone just over a quarter of adults are obese, while a further 41 per cent of men and 33 per cent of women are classed as overweight. Last month, the National Obesity Forum declared that we were in danger of exceeding the 2007 projection that half of all adults will be obese by 2050.

Despite this, the British Obesity and Metabolic Surgery Society has recently warned that many obese patients are being denied bariatric surgery due to lack of access to weight management services, which are a prerequisite to surgery. Meanwhile, the current Quality and Outcomes Framework (QOF) only requires GPs to register obese patients, not to help them lose weight, effectively ‘rewarding’ GPs for keeping patients obese.

With its unparalleled accessibility and growing evidence base for other public health services, it is clear to many that community pharmacy has a big role to play in reducing rising levels of obesity.

Growing evidence

Evidence is building steadily to support the value of community pharmacy-based weight management services.

For instance, the healthy living pharmacy (HLP) evaluation showed positive findings in this area, while a healthy weight service trialled in Portsmouth pharmacies last year involving over 280 patients achieved an average weight loss of 6.3kg per person over the course of one year, with over a third of patients losing 10 per cent of their body weight.

Mike Holden, chief executive of the National Pharmacy Association, believes that community pharmacy’s accessibility, together with the local knowledge of its staff, makes it ideally placed to offer weight management services.

“The key is being able to relate peer-to-peer in an environment that is not purely clinical: I call it a socio-clinical environment. It is less judgemental and threatening than a purely clinical environment but more appropriate than, say, a village hall,” he says.

According to Holden, developing the skills and knowledge of the pharmacy team; offering a service that patients can be easily referred onto or self-refer and that rewards them for outcomes; and developing links with other providers are critical to developing a successful pharmacy weight management service that helps individuals achieve sustainable results.

Be opportunistic

However in the absence of a formal weight management service, pharmacy can still make a significant impact on obesity through opportunistic interventions, either through health awareness promotions or through other services, such as MURs.

Pharmacy brief interventions on alcohol using scratchcards have been shown to be effective at reducing alcohol consumption, and Mike Holden argues that developing similar tools for physical activity, together with increasing staff knowledge of behavioural change through schemes like the health champion course, could do the same for obesity.

According to pharmacist Alistair Murray of London’s Green Light Pharmacy, the best approach towards weight management is to raise the issue “proactively, for example during a MUR, in relation to conditions like diabetes, high blood pressure and heart disease or as part of a NHS health check”.

Once the patient has been weighed and measured and given a print-out with his/her numbers on it, pharmacists can then use motivational interviewing techniques to help the patient change them. “It is easier to talk about the numbers in a health context,” he says. “It is not a judgement call; it not us saying they look overweight – but asking them if they are happy with those numbers. It is like dealing with any other test result.”

Atul Phakey of Phakey’s Pharmacy in Nottingham has found that NHS health checks can provide a useful route to reducing obesity by helping individuals to understand their risk of heart disease and diabetes. The pharmacy, which has provided over 400 health checks in two years, also runs a “private but affordable” weight management service, which Phakey believes could be just as successful with adequate reimbursement.

National service or framework?

Given the need for accessible weight management services around the country, there have been calls for a nationally commissioned pharmacy weight management service.

Alistair Murray welcomes such a move but cautions that a national service would need “more flexibility to match the needs of individuals” and should reflect the variety of pharmacy approaches to weight loss, which may include motivational interviewing, behavioural changes, meal replacement products or weight loss drugs.

With public health services coming under the remit of local authorities, a national pharmacy weight management service is unlikely. However Mike Holden would like to see a national framework to help pharmacies adopt and share best practice in helping their patients lose weight and keep it off.

Reducing obesity

Clearly, eating highly palatable foods overrides the normal processes that control appetite and therefore diets which are based on foods that are less rewarding but more satiating should lead to weight reduction. One such approach is the paleolithic diet, which attempts to replicate the diet of our ancestors and is based on satiating but low calorie density foods, such as lean meat, fish, fruit, vegetables, root vegetables, eggs and nuts.

In a study with type 2 diabetes patients, the paleolithic diet produced more favourable weight loss and improved hypertension compared to a diabetes-recommended diet. In another study comparing the paleolithic diet to the Mediterranean diet in patients with ischaemic heart disease, both groups lost an average of 4kg in weight but there was a greater reduction in waist circumference in those assigned the paleolithic diet. Furthermore, participants found the paleolithic diet more satiating than either the Mediterranean or diabetes diet.

In addition, there is evidence that focusing on satiating macronutrients, such as protein, can lead to significant weight loss. In one study, raising the protein intake from 15 to 30 per cent of calories reduced overall daily calorie intake and increased fat loss.

Although exercise is a poor strategy for weight loss, evidence from rodent studies suggests that regular exercise is effective at reducing diet-induced hypothalamic inflammation.

Ongoing challenge

Considerable progress has been made in our understanding of the neurological basis of obesity. And what has become clear is that simple advice “to eat less and move more” is unlikely to prove successful in the long-term because lowering body fat through dieting triggers compensatory mechanisms to restore fat levels (e.g. we always feel hungry and have less energy) – and these are difficult to override.

Achieving new eating habits is going to remain a considerable challenge given that we are continuously exposed to cheap, convenient and tasty junk food. The battle of the bulge goes on.

Weight loss training

Omega Pharma has developed a weight management training module to help pharmacists and their staff refine their skills and knowledge. Available at Omega Pharma training, the module focuses on category information and advice, scenario-based learning and recommendations, and includes an online test.