chapter 6: eat to improve your immunity – the macros
Macronutrients are nutrients that we need daily in fairly large quantities. They include proteins, carbohydrates and lipids (fat). They provide our bodies with energy, promote growth and repair, and support our immunity and numerous other areas of health. We need to make sure the macros in our diet are balanced, or it can have a significant and adverse effect on our immunity. The macros all have their own functions, although our immune cells alternate between carbs and fats as their fuel source. When we are fighting an infection, their choice of fuel is carbs, but for day-to-day functioning (when we are not battling a cold, fever or infection) our immune cells use fat.
A balanced and nutrient-dense diet is crucial to supporting our immune function. Research has shown that the development and optimal functioning of our immunity is directly influenced by diet. In addition, any deficiency or excess of certain nutrients can affect the number and activity of immune cells, thus balance is vital. As well as ensuring healthy immunity, a balanced diet is also key for promoting optimal gut health. Studies have shown that there is a significant amount of interaction between our body’s immune system and the gut microbiota, and diet is considered to play a significant role in influencing our microbiota48.
Lipids (a.k.a. fats)
Dietary fatty acids are said to have major effects on immunity, and studies have also demonstrated that nuts and other plant-based foods, which are abundant in polyunsaturated and monounsaturated fats, can increase gut bacteria diversity.
The groups of fatty acids that together form fat are called lipids, and are what I am referring to when I use the word ‘fat’ in relation to diet. Fat is as essential to your diet as protein and carbohydrates and has several important functions, such as being an essential building block for our cells, providing energy and the fat-soluble vitamins A, D, E and K. Fats are mainly produced in the liver, and come in a variety of forms to replenish the cells and provide energy for organs such as our brain.
However, not all fats are created equal:
There are two types of fats that have been identified as potentially harmful to your health: saturated fat and trans fats.
Saturated fat
Saturated fats tend to be solid at room temperature and are found in fatty cuts of beef, pork, poultry skin, lard and high-fat dairy foods, such as full-fat (whole) milk, butter and cheese.
In a paper published in the journal, Cell Reports49, researchers found that saturated fat can ‘short-circuit’ both mouse and human immune cells, producing an inappropriate inflammatory response as a consequence. Furthermore, a review of 15 randomized controlled trials (RCT – the gold standard when it comes to evidence) that investigated saturated fats and heart disease concluded that replacing saturated fat in your diet with healthier polyunsaturated fats may reduce heart disease risk50.
According to the British Nutrition Foundation51, even though significant progress has been achieved in working towards the target of getting population intakes of saturated fat below 11 per cent of food energy, there is still quite a way to go. However, there are several easy ways to cut down on the amount of saturated fat in the diet, including:
Monounsaturated fat
Monounsaturated fats, also referred to as MUFAs, are seen as one of the ‘good’ fats able to decrease inflammation and support our immunity. They come mainly from olive oil and rapeseed (canola) oil, but are also found in plant foods like avocados and nuts, as well as meat and animal products. The American Heart Association recommends that the majority of fats you eat should be monounsaturated or polyunsaturated, instead of saturated and trans fats52.
Polyunsaturated fat
Polyunsaturated fats, also referred to as PUFAs, are essential fatty acids, which means they’re essential for normal body functions. As your body can’t make them, you must get them from food. PUFAs help with blood clotting and are also involved in the composition of cell membranes. In addition, they play a very important role in regulating the nervous system, blood pressure and inflammation. The most common types of PUFA oils are sunflower oil and safflower oil.
In their unheated form, PUFAs have been reported to reduce the risk of heart disease, support immunity and exert various other health benefits. However, when they are heated these beneficial effects are cancelled out. Damaged polyunsaturated fats are called ‘trans fats’ and they are the worst type of dietary fat, shown to impact immunity and also fertility in women. There is no safe level of trans fats; therefore they have been officially banned in the United States, Denmark, Austria and Switzerland. Currently, trans fats aren’t banned in the UK; however, the government has chosen to allow food companies to voluntarily reduce the trans-fat content in their products. Although many UK food producers have agreed to omit trans fats, it is believed that some foods still have them, often listed as ‘mono and diglycerides of fatty acids’, so do read food labels carefully.
Foods that may contain trans fats are typically sweet, carbohydrate-based foods or those with relatively short shelf lives.
Trans fats are typically present in the following foods:
There are two main types of PUFA: omega-3 and omega-6 fatty acids. These are both very important nutrients.
Omega-3 fatty acids
Omega-3 fats are known as essential fatty acids and must be derived from our diet as our bodies are unable to make them. They are required for essential functions such as digestion, cholesterol transportation, brain function and blood clotting. They are also vital for our immunity, as they may enhance the functioning of the immune cells.
Omega-3 fatty acids have been shown to decrease inflammation, and a significant body of research has consistently reported a link between a greater omega-3 intake and reduced inflammation. Inflammation is a natural response to infections and is crucial for our health, but when inflammation lasts for a long time it is referred to as ‘chronic inflammation’ and needs to be addressed. Studies have also shown that consuming a sufficient intake of omega-3s during the first year of life is associated with a decreased risk of autoimmunity. Additionally, these super-powerful nutrients have been observed to help treat lupus, rheumatoid arthritis, ulcerative colitis, Crohn’s disease and psoriasis.
Chronic inflammation has been shown to be a factor in nearly all chronic diseases in the Western world.
The three most important omega-3 fatty acids are: ALA, EPA and DHA. You can find ALA in plant-based foods such as walnuts, flax seeds (linseeds) and chia seeds, while you are most likely to find EPA and DHA in animal produce, such as wild salmon, mackerel and trout. We need to convert ALA into EPA or DHA for us to be able to actually use it for optimum health. However, in humans this process is inadequate, with approximately 1–10 per cent of ALA being successfully converted into EPA and 0.5–5 per cent being converted into DHA53. If it isn’t converted, it can be used as an energy source or will be stored as fat.
Omega-6 fatty acids
Like omega-3 fatty acids, these are also essential and you need to get them from your diet. They can be found in most vegetable oils, nuts, fatty meat and some farmed fish fed on soy and corn. The most common omega-6 fat is linoleic acid, which can be converted into other omega-6 fats, including arachidonic acid. As with EPA, our important omega-3 friend, arachidonic acid generates eicosanoids; however, these are more pro-inflammatory, and if there are too many, it may result in increased inflammation.
Although omega-6 fats are essential in the right quantities, the optimal ratio of omega 3:6 has not been well defined, and there are differing views about the ideal ratio. However, recent research has suggested that to improve this ratio, we should focus on consuming more omega-3s in our diet, not less omega-6s. In the UK, intakes of omega-6 (principally linoleic acid) are close to the recommendation of 6.5 per cent of dietary energy51. However, the American Heart Association recommends getting 5–10 per cent of your daily calories from omega-6 fats52.
What does 5–10 per cent of daily calories from omega-6 fats look like? Based on an individual who consumes 2,000 calories a day, this would equate to approximately 11–22g:
Getting your omega-3 fats
While there are currently no government guidelines in the UK as to how much omega-3 fat we should be eating, it is widely accepted that two portions of fatty fish per week is recommended. If you don’t eat fish or are vegan, opt for algae supplements instead. Alternatively, you may wish to supplement, and this is covered in the next chapter (Chapter 7).
Three of my favourite omega-3-rich recipes:
Carbs
Carbs have been vilified in recent years, yet we need carbs in our diet, as glucose is the major source of fuel for the brain and the immune system. We need to focus on prioritizing complex carbs that are rich in fibre, while limiting the highly refined simple sugars, which are found in sweets, chocolate and cakes. Simple carbs are energy-dense (high in calories), yet deficient in nutrients and quickly absorbed. Research has also shown that high-carbohydrate meals may lead to greater oxidative stress and inflammatory response54.
Complex carbs
These healthful dietary components are made up of sugar molecules that are strung together in long, complex chains. While simple sugars, such as sucrose, are absorbed rapidly, complex carbs such as vegetables, legumes and whole grains tend to take longer to be metabolized, thus preventing blood-sugar spikes. They are also lower in calories, while being nutrient dense and providing us with vital vitamins, minerals, phytonutrients and fibre.
An animal model study55 demonstrated that a high-fat, high-sugar diet has an adverse impact on our gut microbiome, which may influence the brain and behaviour. In addition, human studies have reported that artificial sweeteners can exert a negative effect on our blood glucose, because of their influence on our gut microbes. Furthermore, it was demonstrated that aspartame promotes the number of some bacterial strains that are associated with metabolic disease.
Metabolic disease refers to a group of conditions that can raise your risk of heart disease and Type-2 diabetes.
When we are fighting an infection, our immune cells’ preferred source of fuel is glucose. If we don’t have enough glucose, this can impact our immune system’s ability to deal with an infection, and may lead to a reduction in number and function of crucial immune cells56. While balanced blood sugar is crucial for reducing chronic disease risk, it is also paramount for immunity. If blood sugar levels stay high for too long, this hinders our immune cells’ ability to carry out their role and function, which makes us vulnerable to infections. To promote healthy blood-sugar balance, we need to focus on including the best-quality carbs possible, which as we know are the complex carbs (whole grains, beans and fruit). Complex carbs take longer to digest, which means they have less of an immediate impact on blood sugar, causing it to rise more slowly. In addition, they are highly nutritious and loaded with micronutrients, phytonutrients and fibre.
Fabulous fibre
In the 1970s and ’80s, we discovered that there were two main types of fibre – insoluble and soluble. Unlike soluble fibre, insoluble fibre is not fermented in the colon and doesn’t ‘feed’ our good bacteria. However, it is important to our health, and aids with more regular bowel movement. Soluble fibre ‘feeds’ our bacteria and helps them thrive, and this type of fibre has also been shown to switch immune cells from pro-inflammatory to anti-inflammatory, which helps us to heal faster from infection57.
Prebiotic fibre is important for feeding our ‘good’ gut bacteria. If we don’t eat enough prebiotic fibre, this results in an adverse effect on our immunity and may lead to illness58. Therefore, by feeding our gut bacteria, we are also strengthening our immune system.
Inulin and beta-glucan
Two other types of soluble fibre include inulin and beta-glucan, and these also promote the growth of our ‘good’ gut bacteria. Beta-glucan fibre can be found in oats and barley, and studies have shown that it can enhance immune response, as well has exerting anti-inflammatory and antimicrobial benefits59. Inulin-rich foods include onions, leeks, garlic, chicory (endive) and Jerusalem artichokes. In fact, over 70 per cent of the fibre in a Jerusalem artichoke comes from inulin. Unfortunately, people who are intolerant to FODMAP foods are likely to experience side effects from consuming these foods, such as gas and bloating. Therefore, when adding inulin-rich foods to your diet, start with small amounts, as larger amounts are more likely to trigger side effects. If you increase intake slowly over time, that will help the body to adjust.
FODMAP stands for ‘fermentable oligosaccharides, disaccharides, mono-saccharides, and polyols’. They include sugars that may cause digestive discomfort in some people. FODMAP foods include wheat, garlic, onion, watermelon, apples, apricots, cherries, nectarines and plums.
Resistant starch
Another type of fibre is resistant starch, which provides the benefits of both insoluble and soluble fibre. It is also beneficial to our immunity and gut health to include resistant starch in our diets, which our gut bacteria love. This starch can’t be digested anywhere except the colon – hence ‘resistant’. Once it reaches the colon, it feeds the friendly gut bacteria, which then gobble it up and release butyrate. As we know, butyrate strengthens our gut lining, in addition to lowering inflammation. Foods such as cold white potatoes (they need to be cooked then cooled), unripe bananas, legumes and rice (cooked and cooled) are all good sources of resistant starch.
A healthy digestive tract is paramount for the immune system as, if we are continually constipated, there can be a build-up of toxins, which may then be absorbed into the bloodstream. The immune system then has to contend with this, as does the beneficial gut bacteria who move aside for types like Candida, which we want to limit. Without an adequate intake of fibre our immune system can’t function properly. So, try to include as many different coloured vegetables on your plate as possible. Ideally, aim for 25–30 different vegetables (and some fruit) a week: research shows that those who consume a greater variety of plant-based foods have more diverse and healthier microbiomes. We don’t yet know which gut bacteria prefer which foods, so include as much variety as possible.
What does 30g of fibre look like?
Here’s an example of how you can reach your 30g a day goal:
I have included lots of recipes in the book that are rich in fibre, prebiotic fibre and resistant starch. Three of my favourite fibre-rich recipes:
Key points
Protein
Proteins are large molecules that have numerous roles in our body. They are needed for the structure, function, growth and repair of our tissues and organs. Since all our cells contain protein, this powerful macronutrient is critical and helps to promote optimal health and strong immunity. It has been well-documented that protein deficiency damages immune function and increases the susceptibility of animals and humans to infectious disease60.
The amino acids
Proteins are made up of lots of smaller molecules known as amino acids. These are all linked to each other in long chains. It is the order of amino acids that determines each protein’s individual structure and its precise role and function.
There are 20 different types of amino acids that can be combined to make a protein, and our body makes 11 of these, referred to as ‘non-essential amino acids’. However, there are nine known as ‘essential amino acids’ that you must consume in your daily diet because your body is unable to make them. In addition, our clever, friendly gut bacteria can make very small amounts for us.
Getting the right balance of amino acids is vital for our immunity since they are essential to making immune cells, cytokines and antibodies to fight infection.
Complete proteins
These provide all of the nine essential amino acids that your body needs in appropriate amounts. Meat, poultry, seafood, eggs and milk products are examples of complete proteins. When it comes to plant-based protein, I use soy and quinoa a lot in my recipes, as they are considered a complete protein.
Incomplete proteins
These provide some amino acids, but not all of them. Many plant-based proteins are incomplete proteins, and must be consumed together as complementary proteins in order to get all of the amino acids that the body needs. Nuts, seeds and most grains are examples of incomplete proteins. However, by eating rice along with beans, lentils or tofu, you improve the balance of amino acids and increase the usability of the protein.
How much protein do we need?
Since too little protein in the diet may lead to symptoms of weakness, fatigue and poor immunity, it is vital we consume sufficient amounts. In the UK, men and women aged 19–50 need approximately 56g and 45g per day of protein, respectively. People over 65 may benefit from consuming a little more protein – between 1g and 1.2g per 1kg of their body weight – to help minimize age-related muscle loss61.
Protein recommendations are similar in the US, where the recommended intake is 0.8g of protein per kilogram of body weight. This amounts to 56g per day for the average sedentary man, and 46g for the average sedentary woman. However, there are notable exceptions: anyone with severe kidney disease should avoid extra protein; also, weight-lifters and endurance athletes may need more to repair and rebuild their muscles.
What does 50g of protein in a day look like?
key points – nutrition to strengthen your immunity