The Depth of Breadth

Microphilosophy, Slider

When I showed someone my forthcoming book, How the World Eats, the first thing they said was “It’s big!” It is indeed a fat tome, the reason being that it ranges so widely. A work of such breadth can raise the suspicion that it lacks depth. However, I think the assumption that there is a necessary trade-off between depth and breadth is simplistic at best, downright wrong at worst.

Philosophy is the clearest counterexample to this formula. Wilfrid Sellars came up with what is to my mind the best single sentence to describe the aim of philosophy: “to understand how things in the broadest possible sense of the term hang together in the broadest possible sense of the term.” Breadth two, Depth nil. We have come to assume that philosophy is deep and that the adjective is a compliment rather than a description. So it can be shocking to realise that philosophy isn’t really deep at all. It tries to identify the most general principles and so is better described as an enquiry of extreme breadth.

Sellars’ remark is a reminder that different forms of rational enquiry operate at different levels. Consider how to eat. If we are looking for people who can tell us about what is going on at the micro scale, we are spoiled for choice. Soil, nutrients, the gut microbiome, preserving technologies, pesticides: all have been studied in great detail. We also have experts who look at one aspect of the food system at a macro level: economists, ecologists, veterinarians, climatologists, anthropologists and so on. 

But what if we want – to paraphrase Sellars – to understand how the food system in the broadest sense of the term hangs together in the broadest sense of the term? For that we need not a traditional specialist, but a generalist. And to give generalists like myself full respect, we ought to add that there are such things as specialist generalists: people who devote their entire working lives to thinking generally as clearly and rigorously as possible. Joining the dots is a skill as difficult to master as meticulously drawing them.

One thing I hope readers will get from How the World Eats is a clearer sense of the best level or scale to think about the different aspects of the food they eat. Nutrition provides perhaps the clearest example of this. It is tempting to think that in order to eat well we need to zoom in and think about the nutritional content of everything we eat. Indeed, mainstream dietary advice seems to follow this model. You should avoid consuming too many calories, refined carbohydrates and saturated fats, while getting plenty of fibre, vitamins and minerals. 

This is all true, but it is also very, very general. And that’s because nutritional science hasn’t really understood what makes for a good diet beyond such truisms. If you try to zoom in closer and micromanage your nutrient intake, you discover that there are so many known unknowns, it is more trouble than its worth.

Take calcium. Our bones get thinner as we age and this can lead to osteoporosis, which is a risk particularly for post-menopausal women. Calcium can help strengthen bones and so older people especially are advised to get plenty of it. In the UK, the target is 700mg per day. But it is not enough to just look at the calcium content of different foods and pills and do the maths. Not all calcium is equal, because the body absorbs it more or less efficiently, depending on where it comes from and on whether it has enough vitamin D and K. So although foods like spinach, brazil nuts and collard greens are high in calcium, they are not good sources of the mineral because they contain phytic and/or oxalic acids, which block its absorption. There are also good reasons to think that calcium found naturally in foods is absorbed more efficiently than that found in pills.

Of course, we know all of this because of scientists who are narrow specialists. Their work is vitally important. But one of the key practical lessons to draw from it is that the body is so complex that it is hubris to think we know enough to micromanage our diets for optimal health. There are so many ways in which foods interact with each other and the body that tweaking any highly specific variable apparently for the better risks tweaking another for the worse.

To draw the right lessons from nutritional science therefore requires us to view the information we have at the correct level of generality. There are some fairly specific things we can know, for example, around avoiding too much saturated fat and refined carbohydrates. You may also have a health condition for which there is some specific dietary advice. But the most important truths about diet are very general and it is still difficult to top Michael Pollan’s seven word maxim: Eat food. Not too much. Mostly plants. (Note that by “food” he means whole food, not the “edible food-like substances” found in much processed “foods”.)

I want to stress that going back to such general rules  is not a matter of giving up on thinking about nutrition because it is all too difficult. On the contrary: this is the position you reach because you have thought about it as throughly and well as you can, examining the most important evidence. The evidence is that while we know a lot about the general determinants of a good diet, the details remain too complex to untangle.

What’s more, the most important evidence is not the most narrow and detailed. Cutting edge studies do not deliver us with reliable, actionable conclusions. The evidence that counts most is that which is most established, and that supports only the most general advice.

One more thing to bear in mind. Some of the best evidence we have is about the nature of evidence in general. We know that nutritional science is still evolving and that there is much that we still don’t understand. So we ought not to be too confident that anything we know is fully understood and beyond future revision. For example, we know that the categories of mono- and poly- saturated and unsaturated fats are very broad and that there are many differences between the foods that contain them. So we should not be surprised if we find that, although in general saturated fats are to be eaten in moderation, not all are created equal.

My own bet is that those found in minimally and unprocessed whole foods are going to be better for us than those added to processed ones. But it is a bet. That is another feature of thinking about things broadly. Little to nothing is certain and we must follow David Hume’s peerless advice to proportion our beliefs to the evidence. We have to be aware that we are making fallible judgements, not deducing certain truths.

Nutrition is actually just one small part of How the World Eats. There is a lot more about the production, processing, selling and distribution of food. I use nutrition as an example here partly because it is often what most interests people but also because it exemplifies both the need for breadth and how this does not come at the price of rigorous thinking.

My final plea to respect the skilled handler of the broad brush is to ask you to think about how space is relative. What is up and down, left or right, depends on your view point. We imagine depth as the vertical and breadth as the horizontal. But if the horizontal axis is wider than the vertical one is deep, hasn’t the broad thinker gone further than the supposedly deeper one? And if you flip the image I have just painted 90 degrees, you can see that the distinction between depth and breadth is arbitrary anyway. There can be more richness of thought in dense, broad thinking than in shallow, deep work.

Viva las generalistas!

News

You have until 1 October to take advantage of a special pre-order offer for How the World Eats. In association with the independent Max Minerva’s Marvellous Books in Bristol, you can order a signed copy with the bonus of an exclusive free coaster, all with free shipping in the UK. If you are a supporter, you will also be sent a code to get free international shipping, a saving of £7. (So if you game being a supporter and sign up for just one month, you’re up £2 straight away!) Pre-sales can really help to launch a book so I’d appreciate every one. Order here now! In case you need any more persuading, check out just some of the lovely praise the book has already received, which I stress is from people I barely or do not know and who owe me nothing! (I’m afraid this is not true of a great many gushing endorsements.) 

I’ve got a lot of events coming up talking about the book, so here are the tour dates. (OK, I know it’s not really a tour but it makes it more exciting to call it one.) Do say hello if you’re there, whether you buy a book or not.

In addition, I’m hosting two other Philosophy Salons at St George’s Bristol, one on Monday 4 November on what our politicians owe us with Jessie Norman MP and Thangam Debbonaire ex-MP; and another on Thursday 7 November on the positivity of negative emotions in politics with Myisha Cherry and Joanna Burch-Brown. These are terrific events and our salon format has worked very well so I’m really looking forward to these.

That’s all for now. If you’d like to receive future posts like this direct to your inbox, at no charge ever, sign up below. 

Until next time, if nothing prevents.