[Food as Medicine] Food and the brain

Find out how your body controls your appetite and learn more about the eating pattern known as 'food addiction'.

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What is appetite and how can it affect my health?

Appetite can be defined as a natural desire to satisfy a bodily need, especially for food; or a strong desire for something, such as food. (Oxford Dictionary).

The signals

Hunger is the physiological driver of appetite – mostly we recognise this as physical signals from our bodies that it’s time to eat – a rumbling tummy is a signal that our body is seeking food.

In humans, our desire to eat can be driven not just by physiology but by our situation – for example, a delicious cake is available at work to celebrate someone’s birthday – we may not feel hungry at all when it’s time to have the birthday celebration or have little appetite but we may still eat a piece of cake, not to fulfil our hunger but because it is simply available and everyone else is having cake…so we have some too.

Responding to signals

How we respond to external signals to eat differ considerably – for example, some people seek food when they are upset or depressed, in others the exact opposite may occur and negative feelings induce a lack of appetite or desire to eat. A range of cultural issues can also impact on our appetite – for instance a food that is highly valued and desirable by certain people say for example, fois gras, may be very unappetising to another person.

So, our desire to eat is driven not only by physiological signals that tell us we need to eat to sustain our energy intake but a whole host of factors.

Appetite can be affected by a wide range of factors including physical activity, psychological, social and cultural influences. It is a complex area with no simple explanation why everyone eats the food they do… but your own appetite and what drives it is very important to consider when you are thinking about making changes to diet.

To understand what your individual drivers of appetite and food choices are because if you can understand these then you can learn to respond differently to them if you need to.

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What controls my appetite?

Watch Helen talk about the way our mind and body control our appetite, and how that impacts our health.

HELEN TRUBY : video transcript

So if we think about what controls your appetite, is it physiological, simply physiological, or does your mind actually play a role in it as well? It has to be a combination of the two. Obviously, your body's physiology does what it's going to do, and in terms of your gut hormones and things, then you are going to have a sensitivity to those gut hormones. We know that people who are obese compared to people who are lean seem to respond differently to those gut hormones, indeed. And that might, as we've discussed, might not help people who are already overweight maintain weight loss.

Your mind is also important in the fact that we know that people eat in certain situations.So some people who, for instance, might be regarded as emotional eaters will eat for comfort, or they will eat in circumstances where they perhaps eat far too much than they need to. And indeed, they know that they don't need to eat that amount of food. So understanding ourselves as well, understanding our mind, what triggers us to eat, what triggers us not to eat, is really part of that process of learning about how you as an individual are going to be able to manage your weight.

In our work with children who are overweight, we often talk to them about feeling hungry and trying to cue them into signals when they're actually hungry. And children who are overweight and have been overweight for a long time will often say they either always feel hungry or they never feel hungry. They simply eat, because food's in front of them, or there's seemingly a right time to eat. So there are aspects of being able to get more in tune(조율) with your actual appetite and satiety mechanisms. We don't entirely understand how best to do that, but we do know that once people lose weight, they seem to regain some kind of sensitivity to understanding those signals about when they've had enough too eat or not.So some of it is certainly physiological, but there is probably a large element of psychology around it as well in people being able to reprogram themselves as to what's an appropriate amount to eat and when to eat it. And also, our environment is such an obesogenic(비만을유발하는) environment. We're always surrounded by food. We're never more than 20 paces from a vending machine, for instance, and it's very difficult in that environment to actually have some kind of restraint(억제) around food. And I think we often need to learn to have some kind of restraint, but obviously, not become over-restrained, so we're not eating enough, but restraint can be functional in an environment where we simply would all become overweight if we ate everything we wanted to.

So other things that can affect you feeling hungry is the form of the food that you're having your nutrient in. So in terms of if we eat solid food, such as a steak, for instance, or a piece of cheese, that's going to stay in our stomachs for longer, and therefore, it helps us feel fuller for longer.When we have our meals, such as drinks, so if, for instance, we were taking a meal replacement, we would find that that potentially leaves our stomach quicker, and therefore, people might feel a bit more hungry, and they seek more solid food. So some of the diet drinks that people use are quite effective in terms of maintaining or helping people lose weight, and indeed, we have evidence that people who stick to those do just as well as anyone else who sticks to any other diet. But some people find them harder to do.

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Food choices, appetite and the environment

Watch Helen introduce an activity that explores food choices, appetite and the environment.  - survey

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Food and appetite 

Understanding how food works in the body in relation to appetite, satiety(포만) and energy expenditure can be a useful mechanism to harness when thinking about using ‘Food as Medicine’ in the context of weight loss and health.

The energy value of nutrients

Obesity is a state which occurs when the body has accumulated(축적하다) excess body fat. This happens gradually(서서히) over time and reflects a chronic(만성의) energy imbalance whereby energy intake exceeds expenditure.

Energy intake is derived from the consumption(소비) of food and drinks. Different foods and drinks differ in the amount of energy they supply because they are made up of different proportions of macronutrients.

The three main macronutrients: carbohydrate, protein and fat as well as alcohol and dietary fibre, each contributes a different amount of energy. Carbohydrate provides 16 KJ/gram (or 4 calories/gram). Protein provides 17 KJ/gram (4 calories per gram), fat provides 37 KJ/gram (9 calories per gram) and alcohol provides 29 KJ/gram (7 calories/gram).

If your intake of dietary energy is greater than your actual energy needs, this will lead ultimately to fat storage.

Components of Energy consumption

Energy expenditure is how much energy you use up. It is composed of three major components.

• Resting Metabolic Rate (energy needed for body functioning) contributes 60% to 70% of your total Energy Expenditure.
• Physical Activity (energy for body movement) can be quite variable but often makes up 20% to 30% of your total Energy Expenditure.
• Thermic Effect of Food (energy required to digest meals) uses up around 10% of energy expenditure.

Additional energy is also required for growth. The rate of growth is the highest during infancy, then by early childhood growth velocity slows right down until a marked growth spurt occurs during adolescence.

This again leads to higher energy needs, but by 20 years of age the additional energy needed for growth has dropped to zero so any excess energy that is not expended in activity will be stored as body fat.

The energy cost of digesting and assimilating(동화시키다-흡수하다) food

The thermic effect of food is the ‘energy-cost’ required for food to be digested in the gut and assimilated into the bloodstream. This energy cost is sometimes also known as meal induced thermogenesis. Different macronutrients take different amounts of energy to digest and assimilate.

In adults, the thermic effect of protein is 20% to 30%, compared with carbohydrate 5% to 15% and fat 0% to 3%, From this you can see that a high protein meal will require more energy to digest compared to one that is lower in protein.

This fact has stimulated research into whether a high protein diet is better to assist people to lose weight.

What does the body do with food after it is consumed?

In the gut, food is broken down or digested into component macronutrients and absorbed. Absorbed nutrients then follow one of two pathways: they will either be oxidised to provide energy immediately or they will be stored so that they can provide energy at some time in the future. Some macronutrients are more readily oxidised than others.

There appears to be a hierarchy: carbohydrate and protein are oxidised first while fat is oxidised later.

This seems to be because the body does not store protein (protein only accumulates where it is being actively used - which is why you lose muscle if you are not using it) and the body has only a very limited storage capacity for carbohydrate.

Alcohol is also oxidised immediately after it is consumed to try and eliminate it because alcohol is toxic to the body and cannot be stored. In comparison to these macronutrients, fat can very easily be stored in almost unlimited amounts all around the body.

Due to the body’s selection of carbohydrate and protein as first targets for oxidation, carbohydrate oxidation and protein closely track with carbohydrate intake and protein intake, respectively.

In contrast, fat intake does not immediately stimulate fat oxidation but instead can be readily diverted to be stored.

Appetite and Satiety

We eat more food when we are hungry as we respond to our appetite. Different macronutrients seem to differ in their impact on our appetite sensations. Protein quickly settles our appetite and promotes greater satiety or feelings of fullness than carbohydrate and fat.

High protein meals therefore have more ability to reduce energy intake from a meal, as well as intake from the next meal than do meals that are low in protein.

The reason for this difference is that macronutrients are not all equally able to stimulate the release of the hormones from the gut that are required to stimulate appetite. Ghrelin (a gut hormone that stimulates hunger:식욕촉진호르몬) appears to be suppressed more effectively by carbohydrates or proteins than it is by fat.

In addition, protein and carbohydrates are more effective at stimulating GLP-1 (a gut hormone that promotes fullness) than is fat. Protein also induces the strongest release of PYY (another gut hormone that promotes sensations of fullness).

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Is food quality important?

Watch Helen talk about the importance of a diet that’s made up from the core food groups and how they affect our appetite and satiety.

HELEN TRUBY : video transcript

--- (중략) So we know that in terms of overall health, having a diet that's mainly comprised from these core food groups really helps us be able to make sure that we're getting sufficient micronutrients and all those phytochemicals that we're starting to learn more about in our diet. So what we do know is that people far too many of those discretionary foods, so those foods that are high in sugars and fats and high in salt, but are not so good for us. (dougnuts and snacks, sweets etc.)

So what does this tell us about appetite and satiety? Well, as we've discussed, we know that protein types of foods and having these as a part of our diet or a part of our main meals will help us feel fuller for longer, and if we add a protein food in, again, with a bulking agent, so lots of vegetables, for instance, or salads, will help us feel not only fuller for longer, but also provide us with the micronutrients and those important phytochemicals that we need that we wouldn't get any other way. So in that respect, choosing foods from the core food groups enables us to manage and maintain our best of health in terms of the best of what we can do with the genes that we're given, and enable us to meet our micronutrient needs as well.

So in terms of diet quality and how we think about that is that when you're trying to lose weight, you obviously maybe try to eat less, but you don't want to have a low quality diet. So even though you might be able to have a piece of cake, for instance, and it's got the same amount of calories in it as a lunch with sandwiches and a salad, you're actually not going to get the micronutrients you need from your piece of cake. That would be not such a high quality diet, so diet quality really relates to the density of nutrients that you're getting in those choices, and we know that these types of whole foods are going to give you the better choices and being able to make sure that you are getting all the micronutrients you need with also that satiating power, and so it's easier for us to then maintain a healthier weight.

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Food addiction

Food addiction is a term increasingly seen in published scientific literature which is also highly topical in mainstream media. It is an emerging entity which does not yet have a generally accepted definition.

To date it still has not been recognised as a clinically diagnostic condition by either the World Health Organisation’s International classification of Diseases or the American Psychiatric Association’s Diagnostic & Statistical Manual of Mental Disorders.

However, there is an increasing amount of research exploring this possible phenomenon.

Beliefs about food addiction

Over 80% of Australians believe that foods can be addictive and that this addiction may explain patterns of overeating. In fact they consider food addiction as even more powerful than addiction to smoking. People with food addiction are therefore very vulnerable to stigmatisation or becoming the target of negative perceptions.

Research suggests that similarities exist between food dependence and other classic forms of addiction, such as alcohol and drug addiction. Behaviours that have all been associated with ‘food addiction’ include:

• tolerance to large amounts of food
• persistent(고집하는) craving for specific foods
• lack of control over the amount of food consumed.

While a large number of animal studies have been done on food addiction, there are relative few carried out with humans. One result of this is the scarcity of methods now available to detect possible indicators of food addiction.

To date, food addiction has been a largely self-identified and self-reported condition, which has limitations in regards to the reliability and validity of reporting.

Is it a substance disorder(혼란) or is it a behavioural change?

At present, the one most commonly used definition for food addiction is derived from mapping eating behaviours to the Diagnostic Statistics Manual criteria for substance dependence. Symptoms assessed include: tolerance, withdrawal persistent desire, reduction in social activities, increased time and attention to seek food.

Using this method, it has been estimated that as many as 20% of the population may have an eating disorder, with higher incidence among women, people who are overweight or obese, females, those over age 35 years.

People with depression also have a higher incidence of food addiction.

Addictive eating behaviours have largely been examined as one kind of substance disorder. However it has also been argued that food addiction is better called an ‘eating addiction’ and is largely behaviourally based.

Other factors which make food addiction highly debatable(논쟁의여지가있는) is that unlike other recognised substance addictions, people consume foods which provide a complex interaction of ingredients, tastes, flavours, smells, and textures, a very different situation from the consumption of a single addictive substance.

In addition, food consumption is essential for human survival and exposure to food occurs from a young age. This is different from other addictions such as to drugs and alcohol where the addictive substance may not be encountered until adult life.

What types of foods are most addictive?

Very few studies have investigated which ‘foods’ are most associated with food addiction. One Australian study in young adults (18 to 35 years) which used a validated dietary assessment measure found that higher Yale Food Addiction Survey (YFAS) symptom scores were associated with higher percentage energy (%E) intake from energy-dense, nutrient-poor foods including confectionery, takeout foods and baked sweet products, and with a lower %E from nutrient-dense core foods such as whole-grain products and breakfast cereals.

This agrees with other international research where people considered to be food addicted were found to consume more energy (calories) from fat and protein. Other international based research also suggests that not all foods are equally implicated in addictive-like eating behaviors, it is the highly processed foods that appear to be particularly associated with ‘food addiction’.

Currently evidence based treatments for food addiction are limited due to the limited scientific base, however this field is fast progressing. Investigating and understanding if food addiction is real and if it is substance based or behavioural based is key.

Following a balanced diet according to National Guidelines and limiting energy dense foods which are often highly processed are the best recommendations. If you feel or a patient feels ‘out of control ‘with their eating they should consult a dietitian, psychologist and/ or medical practitioner.

Regions

At this point in time, food addiction remains a contentious idea although research and evidence in this area is building.

Results from studies to date suggest that food addiction could be a missing link in understanding the current rates of obesity and assist in developing effective weight loss and weight maintenance interventions for the future.

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• Reference 

Food as Medicine from Future Learn. free courses https://www.futurelearn.com/courses/food-as-medicine

Food As Medicine Online Nutrition Course - FutureLearn

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