The book “Food for Life” from Professor Tim Spector is an excellent review of the relationship between our food and our health. This is a challenging area of medicine. He notes how, even with his medical background, it took his own health scare to start to take many of these dietary lessons more seriously. This is a connection we already all know is important, but for which the details can be confusing. Indeed, Spector opens by highlighting the complexity of the interaction between our health and our food. Many ideas of old are now outdated, although they may still persist in some form or another. Indeed, even the biochemical models don't entirely fit with what we now know. Yes, the idea of macro and micronutrients is still important, but has missing factors. As such, this book focuses on bringing the best of modern evidence into one place.
The Microbiome
Perhaps the most important advances in recent nutrition science have come from understanding the gut microbiome. Older models of health pictured almost all other organisms in the body as potential pathogens, or at best passive agents. The truth would seem that many are actually existing in an almost symbiotic relationship with us; a state of mutual benefit for us and them. These organisms are the microbiome, and those of the gut are most relevant to our dietary health. Some estimates put them as actually outnumbering our own cells. The majority are found in the large intestine, with bacteria being the predominant organisms. However, there are also viruses and fungi which play a positive role, and sometimes even parasites (less commonly, especially in the west).
A major mechanism for their benefits is the enzymatic activity that they undertake. The metabolic arsenal of the microbiome is significantly broader than ours on its own, thus expanding the benefits we can draw from ingested foods. Indeed, it is this activity that seems to be involved in much of the signalling to our bodies that occurs. This signalling is far more significant than we ever previously thought and can even influence our behaviour. It is as if the gut organisms are creating molecular signals to ‘ask’ us for certain foods. These molecules can then go on to have effects on our behaviour, mood, and physical aspects of inflammation and immune system. There are also the local effects that the microbiome has on our gut itself, and the disturbance of it can have major symptomatic effects on our gut.
Some useful terms to consider are prebiotics, probiotics, and postbiotic. A prebiotic is essentially a molecule which is fully or partially undigested by our own digestive system, but which provides nutrition for our gut microbiome. The polyphenols contained in many plants are a good example of an excellent food source, with colouration being a useful guide to content. A probiotic is a food source that actually contains positive organisms for gut health, as can be found in a wide range of fermented foods. Despite the wide belief that stomach acid provides a barrier to ingested organisms, this is not the case, and we can populate our gut through what we ingest. Postbiotic refers to the aforementioned products created by the metabolic activity of the microbiome. Short chain fatty acids are a good example of a class of molecules which seem to impart health benefits, with many others being increasingly understood.
Biology
To further consider the role of food in our lives it is useful to further explore our own biology. We are the product of millenia of evolution and this lens is important for how we consider many features of our dietary health. First amongst this is the importance of our sensory input. This has been specifically honed for food selection as a primary function (the primary function for senses of smell and taste). As such, they interact intricately with our food, including how we select, consume, and enjoy it. The colour impact of a food source seems a strong feature of the visual aspect, and this would seem to correlate well with the polyphenol content of plants and their positive health impact. Our smell is the pinnacle here though. When you think about what it is doing it is really quite incredible. We are able to differentiate between substances with differences down at the molecular level - a phenomenal skill. This allows us to process up to 1 trillion different smell combinations. Our sense of taste has much more overlap with smell than we often realise, although the 5 sense receptors are clearly important. A common myth is that these are limited to certain regions of the tongue, but this is not the case. Indeed, they can be found throughout different regions of the body. Rather, the tongue provides important tactile feedback too, and this is impressively integrated by our brains to give us a detailed analysis of the substance. It is this processing which seems to be influenced by the nature of our gut microbiome, leading to us having certain food preferences and desires. All of this means that our interactions with food are far more complex than we ever thought.
Our individual physiology differences, and their contribution, are increasingly being understood. We are all quite different but, even though we have known about this in medicine for some time, it has been difficult to apply this knowledge. This is especially so in nutrition. Part of this is the uniqueness of our gut microbiome - even in identical twins they are quite different. This leads to variations in how we respond to the same foods, including our circadian patterns and blood sugar responses. Another part is the genetic variation that we have. An example of this is the different forms of amylase that we may possess (the key enzyme for starch digestion). All of this gives strong hints that there will be a role for personalised dietary advice. The most pertinent advice that Spector gives in this regard is around blood sugar monitoring. He advocates using continuous blood glucose monitoring to track your individual response to different types of food. These can be quite different, and indeed can vary notably depending on your personal situation e.g. lack of sleep. This is a good starting point for starting to tailor your diet to your personal response to it, aiming to minimise the foods which cause major blood sugar peaks.
Plants
Probably the most important group of food for our health are plants. The nutritional research can be challenging to unpick, and strong lessons difficult to give, but the signal is persuasive. It is certainly clearer than the evidence for meat or fish. Evolutionarily, plants are some of the hardiest organisms, dealing with a broad range of conditions. The development of a selection of important chemicals, termed polyphenols, have an important role in this regard. These are closely linked to the colour of the plant, as well as to their taste (often fairly bitter). These molecules seem to be of immense value to our gut microbes, and get transformed into molecules that benefit our health effects, like Butyrate. As such, the advice to “eat the rainbow” is a pretty good heuristic when it comes to selecting fruit and vegetables for our diet. We want a good range of plants, and the ZOE study suggests about 30 different types a week is ideal for good health.
Spector also argues that plants bring some key specific benefits which are hard to derive from elsewhere. For example, the nutrient profile of plants seems to be the best mechanism for obtaining our vitamins. Yes, these can technically be obtained through supplements but this is not quite the same. Not only can the quality be variable but it would seem that the mode of delivery is a very important feature of how we take in our nutrition. As the clearest example we can see how the food matrix greatly affects the absorption profile of the contents. This is most obvious for the sugar content of plants, such as fruit. When eaten whole, the blood sugar peak is much lower than if drank in juice form, or even just blended in a smoothie. As such, he advocates that the whole food form would generally be the preferable way to eat such foods, retaining these advantageous profiles.
In addition, the fermentation of plants seems to be a process that adds extra health benefits. Part of this comes from the ‘pre-digestion’ of the food, speeding up the liberation of the contained nutrients - beneficial for both us and our gut microbiome. There is also the proliferation of many of the beneficial organisms that we ultimately want in our gut. Thus, fermented foods are both prebiotics and probiotic. Other fermented foods e.g. kefir, also seem to possess such positive effects, but probably not quite to the extent as with plants. Whilst they are often less common in western diets, Spector advocates bringing regular fermented foods into them where possible.
Unhealthy Food
There is probably a bit more evidence accumulating about what we know is bad for our health. Ultra-processed foods now look to be near the top of this list. These are foods that have undergone a very high level of processing, usually with the addition of a wide range of preservatives, stabilisers, and flavourings, all with the goal of prolonging storage and standardising the product. Indeed, the ultimate goal is a product that has brand recognisability and a strong pull for consumption - the factors which will create profits for the manufacturers. This is quite a unique category of food, as most food does not have high profit margins, or any sense of brand nature. This processing involves a number of steps that seem to lead to negative health effects. The high sugar, fat and salt content, as well as added stabilisers, emulsifiers and flavourings all tend to be common features of these products, and all recognised for their health concerns. However, this is particularly the case when combined together. They push overconsumption of total calories, and the calories they contain often have a rapid release profile, leading to major peaks and troughs in blood levels. There are also concerns about the impact on our gut microbiome. Some components, such as emulsifiers, are essentially antibacterial solvents, and negatively affect our gut flora in ways that seem highly likely to be bad for our health.
Whilst UPFs seem to comprise the pinnacle of foods that Spector feels are the worst for our health, there are additional categories, some of which overlap. These include artificial sweeteners and highly refined starches, and he is also concerned about the nature of snacks with a high sugar and fat load, whether these would count as UPF or not (they usually do). As alluded to, major swings in our blood sugar levels seem correlated with concerning outcomes, including metabolic disease such as diabetes. Foods which allow the rapid release of calories into the blood are the biggest culprits of this, as they cause the peaks, the subsequent excessive insulin response, and the following trough. Refined carbohydrates fit this profile, as does other food without an adequate food matrix - sugary drinks especially. But just the calorie density of many foods is as much of a problem, as the calorie load delivered in a short time is just so large. These are all factors that we should bear in mind when considering the food choices we make.
Storage and Cooking
Whilst we do eat some food in its fresh, raw form, the vast majority undergoes some degree of storage and processing. This does have a reasonable impact on the nutritional profile of the food and so is a key feature to consider. As well as spoiling, a number of foods, especially plants, start to lose nutritional benefits over time. Many historical preservation techniques have been helpful for extending edible time, but not necessarily the full range of nutritional profile. Freezing and canning fruits and vegetables are probably the best approach, retaining key nutrients and prolonging storage time. This is essential if we want to eat foods out of season in an environmentally considerate manner (see below). It is also an important consideration for reducing food waste.
Cooking can have a major effect on the chemistry of food. Indeed, this has been a hugely positive feature of human history as we have moved from the fully raw diet of the rest of the animal world. However, there are also many deleterious effects that can arise from cooking. In many ways this is quite food specific. As a default rule though, vegetables are usually best lightly cooked to minimise nutrient disruption. Excessive boiling in particular should be avoided, as this leeches away large amounts of important components.
Fermentation is a method to both store and ‘cook' our food (of a fashion). The process extends storage life and unlocks many additional health benefits. This is a much more accessible approach to home storing food than some other preservation methods (bar freezing) so can be an excellent option to use up excess plants. Spector encourages us to start to explore the art of home fermentation and discover the health and taste benefits.
Additional Considerations
Environmental considerations are another factor that we should consider within our food choices. This is not just ethical but will have increasing cost and practical implications. Ultimately, growing and sourcing our food sustainably will become essential. This is another reason to move towards a more plant based diet, given the notably lower input needed for the same nutritional output. Similarly, Spector advocates for locally sourced and seasonal products, as they will lack the extra growing and transport costs associated with out-of season products. This may subsequently impact on what food choices we end up making. A good example are avocados, which are a great food with a bad environmental footprint.
Organic food has had a history of being ‘better’, from both a health and environmental perspective. There would seem to be reasonable grounds for believing this, although, as is a pattern in food, there is a certain amount of manipulation of the organic label. In addition, there are some definite and some potential downsides to the approach, including reduced yields and concerns over effects on soil erosion. Certainly there are reasons to be concerned about the effects of pesticides, herbicides, and (especially) antibiotics, but the hard evidence of benefits is hard to find. The extra cost involved may make this tradeoff harder for some people to accept.
How to Eat Healthily
Spector closes the first section of the book by doing his best to summarise health advice around diet. As he notes again, there is a real challenge in using the research base to do this. Even the research that has been done legitimately is often poor quality in its nature, and very vulnerable to bias. Given the power of the food industry, there is also a reasonable degree of ‘propaganda research’, or even outright fraud, that needs navigating. We should bear this in mind whenever we hear health claims, especially when something is being actively marketed.
What we do know is that healthy eating is ultimately a combination of our physiology, our psychology, and our environment. This makes our responses to foods unique, even if there are some common trends that we can detect. Personalised medicine is still a bit of a way off, but there are things that we can start to implement to assess our own unique picture. A starting point is to simply be more reflective and mindful of our diets, taking greater awareness of what we are eating and the effects that it has on our bodies. To take this to the next level, continuous blood glucose monitoring will provide a lot of valuable information on how you respond to different foods. This can allow you to make better food choices, looking to select foods and modes of eating which minimise major swings in blood sugar levels. We can then implement this with the core knowledge we have about many foods that seem well evidenced.
These are probably best summarised as:
Eat plenty of plants - ideally 30 different types per week
A wide range of colours of plants is also a useful heuristic to follow - these tend to represent the beneficial polyphenols
Eat food in its whole form to maintain the food matrix
Avoid ultra-processed food
Look after your gut microbiome - this is a major mechanism for how we can affect our health
Fermented foods are an excellent way to support the health of our gut microbiome.
Eat less meat, and make the meat you eat of higher quality
Preserve and cook food in a way that doesn't compromise the nutritional value.
Specifics
The second half of the book dives into some detailed advice about specific food groups. This provides fascinating advice and information about the apparent health profiles of many of our food staples. There is too much information here to really summarise, but these are some highlights. lights.
Potatoes - Actually less bad than their general reputation. They are highly starchy but this is fine in moderation. They contain a number of additional nutrients e.g. Iron, fibre, but it is actually the skins which have a lot of this - keeping them on is ideal. Indeed, it is the cooking method that is often a problem, as they are regularly fried.
Legumes - Beans, lentils, peas, and peanuts (not actually nuts) are a solid nutritional food. Indeed, when combined with rice (or wheat or corn) you can get essentially all the daily needs of the body, including a good source of protein, a potential challenge with a plant based diet, as well as iron, folate, and fibre. Interestingly, despite the poor reputation of many ‘baked beans’ they are a relatively nutritious and minimally processed food, let down mainly by the added sugar. Overall, legumes are an excellent addition to our diets and we should try and build them into our diets more.
Bread - Also has a bad reputation but has been a staple of human food for almost as long as society. This bad reputation is really just from modern breads with a higher GI index and low fibre in comparison to carbs. This gives those greater swings in blood sugar and fewer prebiotic positives. Sliced loaves are also heavily processed to help storage. Sourdough is the more traditional bread making and generally healthier. The contribution of yeasts and bacteria in the process, as well as the limited ingredients, may be the key for this. As such, buying good quality sourdough, or even making your own, is a better approach than off the shelf, but this is clearly challenging from cost and time perspectives.
Fish - As a contrast, these are perhaps less good than their reputation. They can be a good source of nutrition, especially less common nutrients like omega fatty acids. The quality is very variable though. There are also major environmental and sustainability challenges that should put a considerate consumer off excess fish consumption. Heavy metal concerns are also possible. This is probably only really relevant in the longest lived fish (swordfish, shark) and when high risk, such as pregnancy. The actual evidence for health benefits is also quite scanty. It seems that the smaller fish, closer to the plankton in the food chain, often have the best nutrition profile e.g. anchovies.
Meat - Meat has been a key part of human nutrition through history, but the relationship has changed. We have moved to seeing it as a very regular, perhaps daily, part of our diet, and the quality of the meat would seem to have suffered. This has led to meat that tends to be worse for our health and the environment. There is no good evidence that limited high quality meat is bad for our health, despite oft raised concerns, but this is now an uncommon scenario. We tend to eat regular, low quality meat, and this probably does have adverse health effects, especially around heart disease. Ethical and environmental reasons should push us to eat less, and we would be best served making sure that this is of high quality.
Dairy - Milk is ‘designed’ by evolution to be an excellent source of nutrition for young mammals. This seems to translate to some degree to humans, although the health picture for adults is a little more complex. It does not seem to have some of the health benefits or risks that get attributed to it. Once again, high quality milk in moderation seems a reasonable diet choice. Fermenting it (yoghurt, kefir) does seem to add benefits though, with the additional probiotic gut support. Many yoghurts, especially aimed at children, have a lot of added products which detract from any such health benefits, partly from their direct effect, but also because such probiotic effect is lost. Similarly, many cheeses have a strong probiotic nature. However, they can be even more varied than yoghurts and with an even greater UPF predominance which should be factored in when selecting.
Herb & Spices - These have a traditional association with health, and indeed there are a lot of apparent benefits from use. There are clearly variations between the different types but they are broadly good for gut microbes given their high polyphenol content and fibre. Again, hard evidence for the specifics is scanty though. It seems reasonable to use them liberally with food rather than as supplements, as these would lack many of those general beneficial components. Turmeric has the best evidence of positive health effects as a specific agent, but more evidence is needed before this can be translated into strong advice.
Oils - Spector notes that the clearest signal is around extra virgin olive oil. The PREDIMED study in particular showed large positive health effects. Indeed, he notes that it is probably the closest thing to a true “superfood” that we have. In addition, it seems okay for cooking with, despite a lower smoke point than some other oils. As with other foods, the quality seems to matter - you want good quality, cold pressed. Corner cutting in the production and processing stage seems likely to negatively impact the health benefits.
Other oils would seem to have both a less good health profile and less good evidence base behind them.
Nuts - These look to be a great choice for a healthy snack, with the PREDIMED trial again giving some evidence towards their health benefits. They are fatty, but with many ‘good’ fats, decent fibre and decent protein levels. They also seem to have a good benefit profile for the relative weight being consumed. There are probably several causes for this, including greater satiety compared for the calorie load, low glucose spikes, anti-inflammatory effects and a good gut microbe profile. In short, if you need a snack, a handful of nuts is a very good option.
Seeds are essentially just small nuts with similar health profiles. Flax has the best evidence base of health benefits, but others look like they may be similar.
Salt - Another food that has traditionally been taught as very bad for our health. A lot of this seems to be linked to associations with blood pressure elevations, but the full story is more complicated. Indeed, it is an essential nutrient and impossible for us to be healthy without. There are scenarios where the negative health correlation is clearer, such as patients with diabetes. It is also clear that UPFs tend to have very high levels of salt, which should be avoided. But it does seem that we can probably be more relaxed about our salt intake, and have it as a regular part of our diet, in moderation.