This post, I’d like to focus on what I think of as the ‘building blocks’ of nutrition. Before we can talk about changing or manipulating our diets, or even talk about meals or foods as a whole, it’s important that we understand what our food is made of. These components are referred to as ‘nutrients’ and can be split into macronutrients, which are required in large amounts, and micronutrients, which are only needed in small quantities. Today I’m going to chat to you about the big guys: macronutrients.
Macronutrients include carbohydrates, proteins and fats. Together, they provide our bodies with the energy (calories) they need. It is worth noting that alcohol also provides us with energy and is also considered a ‘food’¹.
Most people will have heard of these, especially those with a penchant for diets which may have you cutting your intake of one macronutrient or another. However, each of these macronutrients are essential for our bodies, and each serves a different purpose. Furthermore, it’s improbable that a food will contain only one macronutrient, rather, foods are made up of a variety of carbohydrates, fats, protein and water¹. Consequently, cutting out entire nutrients is complicated business and it’s my opinion that, unless clinically indicated or medically supervised, we focus on eating a balanced diet comprising all three.
Carbohydrates (CHO) provide the main source of energy in most human diets, contributing between 35-60% of calories in adults in the UK, and between 40-85% worldwide. They influence digestive function, blood glucose control (blood sugar) and satiety (‘feeling full’)².
There are 3 main groups of carbohydrates¹:
- Sugars – (including mono- & di- saccharides, polyols) found in fruit & veg, table sugar, milk, soft drinks, confectionary & other manufactured goods
- Oligosaccharides – which we cannot digest, but are fermented by gut bacteria, found in legumes (pulses and beans), onions, fennel, asparagus and sometimes added to foods as ‘prebiotics’
- Polysaccharides including:
- Starches – found in cereal foods e.g. rice, pasta, bread & potatoes & some unripened fruits
- Non-Starch Polysaccharides (NSP) – or ‘dietary fibre‘ – which we cannot digest, but are fermented by the bacteria in our colons (which can then provide us with energy), found in fruit & veggies, fruit, wholegrain cereals and bran e.g. Weetabix, wholemeal rice/bread/pasta, and pulses²
This can all sound a bit confusing at first, note that the groups above are divided by chemical structure (i.e. the number of glucose units in their chain). Another way to look at it is to determine whether or not we are capable of digesting the carbohydrate; in which case we can compare ‘digestible/available carbohydrates’ i.e. sugars & starches, and ‘non-digestible/unavailable carbohydrates’ i.e. oligosaccharides & fibre³.
Digestible carbohydrates are readily broken down into glucose and absorbed into the blood stream, leading to an increase in blood glucose levels – e.g. that ‘sugar high’ you get after eating a packet of Haribo. The impact on blood sugars will correspond to the meal ingested, for example cold potato salad as part of a meal is unlikely to impact your blood sugar the same way drinking a litre of Fanta might.
On the other hand, non-digestible carbohydrates are not readily absorbed, and make their way down to your colon where they are fermented by our gut flora (bacteria), meaning they do not affect your blood sugar.
The impact of the CHO on your blood sugar determines its ‘glycaemic’ activity, which is where the role of glycaemic index (GI) comes into play. The GI system was originally concocted by Jenkins et al (1981), and indicates how quickly a carbohydrate-food is absorbed and therefore how much of an effect it will have on blood glucose levels. Since, comprehensive GI ‘tables’ have been devised by Foster-Miller and Brand-Miller (1995) and Foster-Powell et al (2002). Limitations of the concept are evident; i.e. the amount of food likely to be consumed is not considered, underlying pathophysiology of the individual is not taken into account (e.g. pre-existing insulin resistance), and furthermore eating more than one food simultaneously (i.e. in a meal) will result in a different glycaemic effect compared to eating each item independently. Despite this, the system can be useful as many ‘low GI’ foods correspond nicely with ‘healthy eating’ guidelines, as they often comprise unprocessed whole-grains, fresh fruit and veg, salads and dairy foods. Foods abundant with ‘free sugars’ – e.g. sugars added in manufacturing to fizzy drinks, ready meals and confectionary, are likely to have a high GI as these sugars are readily absorbed into the blood stream.
So there you have it; a brief overview of the ways we can classify carbohydrates. We can look at their chemical structure, and split them up depending on how long their glucose chains are; we can decipher their digestibility; or, we can look at what they do to the sugar levels in our blood. Or we can look at all three. Luckily, there are guidelines out there, so you don’t need to be a nutritional master-mind to implement this in your diet…
Guidelines – from the SACN report on Carbohydrates & Health, 2015
- Carbohydrates should contribute 50% of your daily energy intake
- Recommended intakes for fibre have been increased to 30g/day, up from the previous 18g/day
- ‘Free sugars’ should exceed no more than 5% daily energy intake (~100 calories from free sugars per day if consuming 2,000 calories per day) – NB this restriction is advised on the basis that reducing free sugars will help us, as the general population, avoid consuming excess energy conducive to weight gain. This refers to the ‘free sugars’ added during manufacturing e.g. in fizzy drinks, in addition to table sugars and fruit juices. It does not refer to sugars found in whole fruits or vegetables and does not include sugars found in milk.
In practical terms, here are a few ideas of the foods which fit into each category. Wholegrain foods including wholegrain bread, rice & pasta as well as other whole grains including quinoa, barley and millet are ideal sources of carbohydrate to help you reach your 50% guideline. These foods tend to have a low GI (do not lead to a spike in blood sugar), provide more nutrition than their refined, white counterparts and also help you to reach the recommended 30g fibre/day.
Proteins are referred to as the ‘building blocks’ of the body, and are made up of amino acids. They are paramount for normal growth, repair and maintenance of health, and are found in large quantities in the muscle, skin and blood⁴. Dead skin, hair and nails are also formed from proteins, contributing to protein losses which need to be replaced⁵. They are also needed in smaller amounts for biochemical processes within the body e.g. in hormones, as part of our cells and to digest fats.
There are 20 amino acids, which can be arranged in a never-ending number of sequences to determine the function and structure of the protein¹. All of these amino acids are crucial for normal metabolism, however we only rely on dietary intake for 8 of these- others, our bodies are able to make in adequate amounts. The amino acids that we must get from food are termed ‘indispensable’ or ‘essential’ amino acids, and those that we make ourselves are referred to as ‘dispensable’ or ‘non-essential’. In some cases, such as illness or childhood growth-spurts, we can no longer form enough dispensable amino acids, and we begin to rely partially on foods; we call these ‘conditionally indispensable/essential amino acids’⁴ .
The individual amino acids we obtain from our food depends on whether they are animal or vegetable derived. Foods that provide close to all of the amino acids humans require are said to be ‘high quality’ proteins, with a high biological value and are found in animal products such as meat, dairy and eggs. Foods that provide amino acids in different proportions to what humans require are said to be ‘low quality’ proteins, with a low biological value. These are likely to be found in plant based foods such as cereals, nuts & seeds, potatoes and legumes. However, by combining foods in a meal you increase the biological value of the protein, for example hummus with bread, cereals with milk and beans on toast are all good vegetarian sources of protein¹ .
In the UK, we get most of our protein from animal products (62%) followed by 23% from cereals², and as a population it provides 15% of our daily energy intake (12% for veggies and vegans)⁵. But how much do we actually need?
In order to quantify the amount of protein we require in our daily diets, Rand et al (2003) carried out a meta-analysis into how much protein was required in order to reach an ‘equilibrium’ in our bodies- i.e. the amount of protein consumed balances the protein being utilised & lost. The resulting recommended daily intake (RDI) for healthy adults was 0.83g/kg body weight per day. So, for example, if you weighed 65kg you should be aiming for about 54g of good quality protein per day⁴.
However, the UK Dietary Reference Values (DRV) published in 1991 recommend a slightly lower 0.75g/kg body weight per day² .
Please note that these recommendations are based the general, healthy adult population and there are situations where higher protein needs are indicated. Some elite athletes or keen gym-bunnies aim for higher protein intakes, however the evidence for whether this is beneficial or required is not concrete, and is worthy of its own blog post.
Here in the UK, protein intake is usually in excess of these recommendations and protein deficiency is usually seen as more of a problem in developing countries, or alongside other problems such as AIDs, tuberculosis, anorexia nervosa or cancer cachexia².
So how do we ensure we are getting adequate amounts of protein? Chances are, if you’re eating a varied diet, you’re meeting your requirements. If you want to up your intake, here are some ideas to give you a protein boost…
Figures taken from Carbs & Cal Pocket Counter in association with Diabetes UK, 2nd Edition (2013)
Other high protein food ideas include most meats (turkey, lean minced beef, pork chops, steak), cheese (especially cottage cheese/low fat varieties), nuts & seeds, beans & pulses, and meat substitutes made with mycoprotein e.g. Quorn.
Fats (lipids) and fatty acids have structural, storage and metabolic functions. Fat has had some bad press owing to associations between excessive dietary fat, obesity and cardiovascular disease, however, fat consumption is crucial for:
- Providing us with energy
- Supplying essential fatty acids (‘EFAs’)
- Absorbing fat-soluble vitamins A, D, E & K and antioxidants, such as carotenoids
- Insulation of our internal organs
- Structural components of our nerves and cells
- Hormone synthesis
- Providing a ‘reservoir’ of energy in the form of adipose tissue (fat stores) for times of inadequate caloric intake²
As such, we can see that we need to eat fat. The issue here lies with the types of fat we consume, as different types of fat are handled differently by our bodies…
There are 3 main types of fatty acids:
- Saturated fatty acids (SFA) – carbon atoms are linked by single bonds only, meaning they are more chemically stable (i.e. usually solid at room temperature). SFAs are primarily found in animal products e.g. fatty meats, lard, and full-fat dairy foods including milk, butter, cheese, cream and yoghurt. They are found in some vegetable foods, too, including coconut and palm oil. These are the fatty acids which have been shown to increase total cholesterol levels in the blood, and in turn are linked to atherosclerosis (build up of plaque in the arteries) and cardiovascular disease².
- Monounsaturated fatty acids (MUFA) – carbon atoms are linked by single bonds with one double bond only, meaning that they are usually liquids (oils) at room temperature. They are also present alongside SFAs in meat products, but highest concentrations are found in olive oil (oleic acid) and rapeseed oil¹. These fats are considered beneficial to health as they do not increase cholesterol levels, and actually work to reduce certain cholesterol levels in the blood if eaten instead of SFAs².
- Polyunsaturated fatty acids (PUFA) – carbon atoms contain two or more double bonds, again making these fats liquid (oil) at room temperature. The presence of >2 double bonds reduces the chemical stability of these oils, and makes them more susceptible to oxidation. PUFAs include both omega-6 (n-6) and omega-3 (n-3) fatty acids, which you have probably heard a lot about; they are both ‘essential fatty acids’ (EFA). This term, similarly to the use of essential amino acids, means that we rely on food to obtain these fatty acids as our bodies are not able to produce them. Although they are both PUFA, they function independently:
- Omega 6 fatty acids are the most prevalent PUFA and are found in veggie oils such as sunflower, safflower, corn, palm, groundnut, rapeseed & soya oils⁵. These fats have been shown to reduce cholesterol levels in the blood, and are necessary for skin health, however excessive intakes are not recommended. As mentioned above, these fatty acids are prone to oxidation in the body, and this process can produce compounds called ‘free radicals’ which can have detrimental effects on health².
- Omega 3 fatty acids have been the subject of a lot of research, and have functions within the human brain and retina⁵. The most prevalent form of omega 3 (named ALA) are present in canola, walnut, soybean and flaxseed oils. Once consumed, our bodies can convert this ALA into 2 derivatives, EPA & DHA, which can be found pre-formed in fish oils, found in oily fish such as sardines, salmon and mackerel¹. Omega 3 does not affect our cholesterol levels, however there is evidence to suggest that omega 3 (especially EPA & DHA) fatty acids have anti-thrombotic (i.e. helps to reduce blood cots) and anti-inflammatory properties, which may act to protect against heart disease².
So now we know about the different types of fat and where to find them, how do we practically implement this into our habitual diets?
We need to ensure we are eating enough fat to a) meet our energy requirements, b) provide adequate fat soluble vitamins and c) supply us with our essential fatty acids. For most healthy adults (not including pregnant or lactating women) this converts to around 15% of our total daily energy intake, with at least 1% from omega 6 and 0.2% for omega 3⁴.
However, note that these recommendations are set at levels needed to cure deficiency, and not necessarily at levels to achieve optimum health. Research indicates that higher levels of omega 3 fatty acids may be beneficial, with suggestions of 0.5-1.8g EPA & DHA/day² (for reference, one can of sardines provides 1.8g omega 3).
The UK DRVs outline the recommended intake as a proportion of daily energy intake, as follows² :
- Total fat should provide no more than 35% daily energy intake
- Saturated fats should provide no more than 11% daily energy intake
- Monounsaturated fats are recommended to provide 13%
- Polyunsaturated fats are recommended to provide 6.5%
So in short, total fats should contribute more than 15% but less than 35% of our total daily energy intake.
So, this blog post was really just me trying to outline the principle functions of the three main macronutrients in our food. I personally think that this stuff is really important to try and understand. My main take-home point is that fats, proteins AND carbohydrates all have essential roles in our body, and so cutting out or drastically reducing even one of these food groups will have consequences on the way your body functions. I hope that it demonstrates the value of a balanced diet over short-lived fad diets. I also hope that for some of you it helps you to clarify which foods fall into which category, which may help to implement the guidelines that are out there, and to show that not all ‘carbs’ or ‘fats’ are created equal.
Thanks for reading! Feel free to leave any comments, criticisms or questions below!
¹Department of Health, (2012). Manual of nutrition. 12th ed. Norwich: The Stationary Office.
²Thomas, B. and Bishop, J. (2007). Manual of dietetic practice. Oxford: Blackwell Pub.
³SACN, (2015). Carbohydrates and health. [online] Public Health England. Available at: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/445503/SACN_Carbohydrates_and_Health.pdf [Accessed 25 Jul. 2015].
⁴Mann, J. and Truswell, A. (2002). Essentials of human nutrition. Oxford: Oxford University Press.
⁵Sanders, T. and Emery, P. (2003). Molecular basis of human nutrition. London: Taylor & Francis.
Header image source: http://gaugegirltraining.com/