This blog is an interim collection of concepts that are important about nutrition.  This is not CPOC nutrition guidance – which will be published in due course.

Introduction

Nutrition literally provides the fuel for life and the building blocks to recover and rebuild following surgery. People with poor nutrition are far more likely to have complications including infection and failure of healing. They are also at greater risk of other problems with pressure sores, weak muscles limiting mobilisation, lengthy hospital stay, re-operations, readmission and additional on-going dependent care. Unfortunately, too few patients get the benefit of good nutritional optimisation. Healthcare staff often feel they do not know enough detail or may be worried that they will appear to be body-shaming. This is a simple guide to some general aspects of nutrition around operations. We should aim for ALL staff to have knowledge and skills to give simple general advice to most people and to identify the small proportion of people who need specialist nutritional help. Some dietary information in the past has appeared contradictory, which means people are more reluctant to discuss it. Often information aimed for patient use can be useful for ALL staff, including reception, administrative, managerial and clinical support staff, so they know that the simple messages they are giving are correct (see Table 1). There is more detail in Table 3.

Table 1: Simple nutritional messages

The physiology of nutrition:

Food is our fuel to enable us to get energy and the building blocks for repair. Some items, particularly small molecules like alcohol, water and sugar are rapidly absorbed from the stomach and first part of the gut. The bulky foods are broken down further on in the gut into smaller molecules which are absorbed (see table 2).

Table 2: What happens to the main food groups:

Control systems – understanding these can help us adapt:

There are multiple mechanisms in the body aiming to give balance – the body detects a level and then causes hormones to be released or nerve impulses to send messages to cause a change. Examples of control systems are:

• Sugar causes a spike of the hormone insulin, causing the sugar to be stored – the body can only store 400 grams as glycogen (in liver and muscles) and amounts above this are converted to fat. The spike of insulin can cause a feeling of hunger a couple of hours later.
• It is usually better to get minerals and vitamins from food sources where possible. For example, if someone takes iron tablets frequently, the body detects this and increases the production of the hormone Herceptin that reduces the absorption of iron from the gut and the recycling of red blood cells.
• When you eat, there are hormones that tell the brain that you are full. This is “satiety”. They take 20 minutes to work. If you eat slowly, and eat a small portion size, you are less likely to over-eat.
• The “gastro-colic reflex” means you may want to have a poo 20 minutes after a big meal.
• “Specific Dynamic Action” means you feel warm after eating a protein meal.
• Hormones often act in groups, a bit like switches – you are either in a “fed” mode or a “fasted” state. The presence of insulin after eating, for example, means your body is trying to store food and is less likely to be using fat stores as fuel.
• Ultra-processed foods are often full of sugar and salt and of a consistency that means they are eaten quickly.

The effect of disease on nutrition:

• Stress and infection can cause the body to break down, rather than store and use nutrients. This is sometimes called a “catabolic state”,
• Steroids are natural body hormones, but they are also drugs that are given to patients with inflammatory conditions or alongside chemotherapy. They can make people feel hungry. They often mean that fat is stored in the belly, rather than arms and legs.
• Chemotherapy can make people lose their appetite. It can also cause sores in the mouth or gut, making it more difficult to absorb nutrients.
• Bariatric surgery, such as ‘gastric band’ can stop people absorbing vitamin B12.
• Coeliac disease is an immunological disease with changes in the gut lining if gluten (found in wheat) is eaten. This reduces absorption of food and minerals, for example people with coeliac disease may have difficulty absorbing iron.
• Pica is the compulsive eating of non-nutritive substances - often associated with iron deficiency.

Causes of food behaviours

There are different food behaviours and cultures. The food environment and cost contribute to what we eat, including advertising, politics, junk food, ultra-processed food and having food presented or priced to appeal. Taxes to disincentivise consumption, such as the sugar tax or minimum unit pricing for alcohol and planning regulations can be helpful in changing the food environment.

Alcohol

Alcohol is a small molecule “ethanol” that is absorbed quickly. The liver can only metabolise one unit per hour. It is converted in the liver to acetaldehyde which is toxic. It is then converted to other smaller molecules using different enzymes. Alcohol has several effects that make it worse leading up to an operation. It changes how drugs are metabolised, meaning you may need more anaesthetic drugs. It reduces inhibitions and makes people more likely to fall. It causes swings in sugar metabolism. It causes weight gain as it contains significant calories. It is better to reduce alcohol before surgery. Consider alcohol-free days, alternating alcoholic with non-alcoholic drinks, and fewer drinks per session. Anyone who is pregnant should avoid alcohol as it crosses the placenta and alters the baby’s brain, causing irritability and fetal alcohol spectrum disorder. Support is available to people (e.g. AlAlon) who are worried about a family member or friend’s drinking.

Effect of exercise on metabolism

Exercise alone does not cause people to lose weight. It is not as simple as calories in versus calories out. Some companies that manufacture fast food, sugary drinks or alcohol like to associate themselves with sport and advertise at sporting events to normalise their consumption. Exercise can help people to stick to a schedule and has a strong “feel good” factor that helps re-shape other habits. During exercise, fat is broken down by β-hydrolysis – this has a quicker onset and is much more pleasant than ketolysis, which is fat breaking down into ketones after many hours of starvation.

Hydration

• It is important to drink enough water.

• Excess fluid causes hormones to change, so the kidneys make more urine.
• Caffeine adjusts the hormones, so you get more dehydrated.
• Beware of over-hydration, meaning too many trips to the toilet especially at night – this can be disorientating for people, especially older people in an unfamiliar environment.
• If dehydrated, the gut absorbs fluid better if it is attached to small molecules, as these are absorbed into cells by active transport with water (8 level teaspoons of sugar and one level teaspoon of salt to one litre of water is W.H.O. recipe).

How to change food behaviours:

Modifying food behaviours has a similarity with changing other behaviours, such as increasing exercise, smoking cessation and alcohol moderation. It is not sufficient just to give information.  People need to see the practicalities of how it will work for them, and to keep the vision of why they are changing. They need to consider what they have in the house, plan ahead, know that each craving only lasts for 90 seconds, have a plan for when they fail, enlist the help of family, friends and partner. Although finances can be limiting, carrots, tinned tomatoes and frozen peas are cheap. Ideally there should be education about healthy cooking and nutrition. Some cultural adaptations are needed – for example some South Asian diets have excessive saturated fat and high G.I. foods, so simple swaps can be helpful. Many aspects of behaviour change, and psychological reframing are linked. Making Every Contact Count training involves amplifying the patient’s own “change talk” and deflecting the “sustain talk” with which the person tries to justify their current habits. Useful steps include Engaging, Focusing, Evoking, and Planning.

Obesity:

People living with obesity have a higher risk of complications of surgery. They are more likely to have Obstructive Sleep Apnoea and type 2 diabetes, blood clots, high blood pressure, infections and delayed gastric emptying risking the airway with an anaesthetic. Many people living with obesity have often tried to lose weight. The Obesity Health Alliance states that “the assumption that our body weight is totally under our voluntary control goes against scientific evidence and results in public health policies that focus entirely on personal responsibility, incorrect messaging in the media and undermines access to evidence-based treatments that would improve the health of people living with obesity” and recommends that health and care professionals should receive comprehensive training in discussing weight and disordered eating with confidence, in a sensitive and non-stigmatising way and be able to assist patients to access appropriate services, including a) an understanding of the complexities of obesity and b) the implications of weight stigma in healthcare environments. It encourages all clinical staff to complete appropriate training on the damage of stigma and how to discuss weight and health appropriately with patients.

Obesity is defined as Body Mass Index (BMI) over 30 (weight in Kg divided by height in metres, squared). Screening and offering brief advice to motivate behaviour change is most effective when patients are also referred to behavioural weight-management programmes. There is evidence that some people can reduce their weight with:

• Ultra-low calorie diets
• Low carbohydrate diets (replacing carbohydrates with fibre, protein and some fat). New studies suggest these can reverse diabetes: www.nutrition.bmj.com/content/3/2/285 and www.gov.uk/government/publications/sacn-report-lower-carbohydrate-diets-for-type-2-diabetes The principle is that:
  • Carbohydrates are converted to sugar then fat
  • Carbohydrates cause you to feel hungry a couple of hours later
  • Protein, fat and fibre help stop you feeling hungry
• Intermittent fasting or having clear time windows for eating. The principle is that the body is either using fat or storing it (and cannot do both) so exercise before eating aids weight loss and larger gaps between eating is better.
• Medication, such as GLP-1 agonists, and bariatric surgery are effective but their role before surgery is unclear and the balance of risks versus benefits would require specialist input.

BMI (weight squared divided by height, with over 30 = obese) is a crude measure. For the future, body composition monitoring should become routine pre-operatively – giving each patient a read-out of their weight, lean muscle mass, total body fat and fat distribution. This would involve machines in different NHS settings. It might help distinguish recognise between people who have heavy ducles with muscle stores (which is good before surgery) or provide an incentive to change exercise and food behaviours even though weight may not change.

Poor quality nutrition:

• Some people are underweight or have diets low in fruit, vegetables, nuts, oily fish and protein.
• Sarcopenic obesity means having a low amount of muscle, alongside excess body weight. There is a danger that weight loss will lead to further muscle loss. The principles (Table 1) are the same. Many would benefit from individualised dietician advice.
• People admitted for emergency surgery can have poor nutrition. If they are in a catabolic state, they may need increased calorie intake.
• Malnutrition means being underweight or with poor muscles in conjunction with a reason causing this (such as nutritional deficiency or disease state).

After surgery

Most patients should aim for early oral nutrition after an operation. ‘DrEaMing’ aims for drinking, eating and mobilising within 24 hours of surgery. Factors that exacerbate stress-related catabolism or impair gastrointestinal function (e.g. opiates) should be reduced. Early mobilisation helps facilitate protein synthesis and muscle function.

Specialist assessment and optimisation

All patients should undergo quick nutritional screening and be given generalised advice. Those identified at screening as being at high risk should undergo nutritional assessment by a registered dietician for individualised optimisation. (See Table 4)

Table 3: Types of nutrition:

Controversies – my views

There are contentious areas. This may cause people to be confused and do nothing. E.g.:

• Carbs: The ‘Eat Well Plate’ has 38% of calories from carbohydrates. I think this contributes to obesity and type 2 diabetes. Carbohydrates are fuel for activity. Excess carbs cause rebound hunger and are stored as fat. Low carbohydrate diets can help with weight loss, reversal of type 2 diabetes, and preventing weight gain.
• Fat: I feel this has been unnecessarily demonised. There are some essential fats. There is a link with healthy fats and better mental health.
• Plant-based foods: These may be healthier if they contain more vegetables, but some vitamins and minerals are not found in plant sources (B12 especially). There is a risk of high carbohydrate intake, especially if people have a low income or fewer options. Some vegan foods are ultra-processed and should be avoided.
• Intermittent fasting seems to be helpful for some people, for example in getting the body to switch from storing to using stores.
• Cholesterol: Much cholesterol is manufactured in the body. Specific foods should not be demonised (e.g. eggs contain useful nutrients).

Individualised advice

All patients should receive general advice. For patients with complex issues, registered dieticians can give individualised advice. It can be helpful for all clinical staff to be able to undertake a basic screening of nutritional status to target advice and suggest interventions.

Screening

The commonest screening tool is “MUST”. In my view, this is not ideal because of the increasing prevalence of obesity and emphasis on unplanned weight loss.

Step 1: Measure height and weight to get a BMI score

Step 2: Note percentage unplanned weight loss

Step 3: Establish acute disease effect and score all from

Step 4: Add scores from steps 1, 2 and 3 together to obtain overall risk of malnutrition.

Step 5: Develop care plan.

Scoring is at: www.bapen.org.uk/pdfs/must/must_full.pdf

ESBEN guidance

The European Society for Clinical Nutrition and Metabolism (ESBEN) issued guidelines on nutrition around surgery in 2017, summarised in Table 4. This seems specialised. CPOC is writing guidance that will include aspects of nutrition from a multidisciplinary perspective.

Table 4: Extracts from ESBEN guidelines:

Further information

• There is excellent advice and posters on the Association of UK Dietitians  
• Obesity Health Alliance
• Book: Ultra-Processed People: Why Do We All Eat Stuff That Isn’t Food … and Why Can’t We Stop? Chris van Tulleken 2024. ISBN: 9781529160222
• Book: The Power of Preparation for Surgery. Dr Sunil Kumar with Dr Toni Brunning 2024 ISBN      979-8878187879