Last week, the UK National Obesity Forum caused a furore by claiming that eating fat, including saturated fat, will help cut rates of obesity and type 2 diabetes. Public Health England hit back, calling NOF's advice "irresponsible".
There's wide agreement that modern diets have led to a rise in illnesses such as coronary heart disease and type 2 diabetes. Like most research, the recent controversy focuses on whether specific nutrients are the cause.
I'm not qualified to decide whether fat is good for you or will help you lose weight. But as a philosopher, and someone who has studied diet and health-related behaviours, I am curious about the question. What we ask determines what sorts of answer make sense. Does it make sense to focus on nutrients such as fat or carbohydrates, for example, or should we reframe the question?
There are many ways to think about the dietary changes in Western societies over the past century or so. Of course, we can think in terms of nutrients: more sugar, more refined carbohydrates, more animal fats, more oils. Another change is in terms of agriculture and animal husbandry: new fertilisers and pesticides, new ways to feed and breed animals, new ways to hasten their growth. A third sort of change starts with an organisational revolution: large corporations now dominate our food supplies.
These corporations are armed with factories and laboratories, with brands and trademarks and marketing departments. And they have created a new sort of food: the ultra-processed variety.
Raw ingredients are reduced to pulps and powders and concentrates and extracts. Chemicals are used to emulsify and enhance flavours (some of these familiar, such as salt, others unknown before modern chemistry). New technologies pound and process and bleach and coat, change liquids into pastes or solids, extract the last scraps from animal carcasses, and "fortify" with vitamins lost in earlier stages of processing.
We see appealing pictures of farms and crops on the packaging, but we've no idea how the products inside came from the baffling lists of ingredients.
Given these enormous changes, how can we discover which aspects of modern diets are damaging to health? I've just sketched out three major changes. But each of them involves many factors. So it is enormously difficult to establish which aspects of modern diets have increased rates of some illnesses.
This isn't to say that conventional questions about different nutrients are unanswerable. Some answers are becoming clear: lots of sugar isn't good for us; trans-fats are definitely bad for us. But just focusing on nutrients is a mistake. In particular, there are good reasons to think that modern food processing itself poses health risks.
Some of these problems overlap with concerns about specific nutrients. Adding salt, sugar or fat (sometimes all three) is a good way to make cheap ingredients palatable. Processing foods tends to remove the many micronutrients found in whole foods, and crops from modern industrial agriculture tend to be poorer in micronutrients anyhow.
Some problems overlap with concerns about energy intake. Processed foods tend to contain less water and fibre, so they are more calorie-dense and easier to consume in large quantities.
Alongside convenience, processed foods are carefully engineered for immediate appeal. They are also marketed with every trick in the book (unlike whole foods). All these factors encourage over-consumption. And then we can add suspicions that some aspects of modern food processing - various additives or "processing aids" or chemicals in packaging - pose health risks of their own.
Don't focus on specific nutrients
Focusing on specific nutrients such as fat or cholesterol has often damaged the reputation of whole foods. Many people limit their consumption of eggs, butter or red meat, for example. Processed food companies are in a better position to defend their products, though. Packaging can easily make or insinuate health claims. Margarine might be made who-knows-how with industrial trans-fats, but it can be formulated to be low in cholesterol to reassure us of its health value. The breakfast cereal might be over a quarter sugar, but the packaging emphasises the fibre or vitamin or iron content.
No one can see or taste nutrients themselves. To focus on them means trusting labels and mistrusting your senses. Confused, we pick up a low-calorie fizzy drink, then choose a low-fat yoghurt that contains all the sugar we just tried to avoid. When healthy eating guidelines focus on nutrients, we become more susceptible to the processed food and drink industry.
Claims that "fat won't make you fat" make headlines. I think they hide a more important idea also hinted at in the new report. On top of modern industrial agriculture, industrial food processing represents the biggest change to human diets since people began farming. Major food and drink companies compete with one another. But as Carlos Monteiro, a professor of nutrition and public health at the University of São Paulo, remarks, "they all have the same overall policy" - promoting ultra-processed foods.
Instead of asking about specific nutrients, we might also ask whether the rise of processed foods has contributed to the rise in diet-related diseases. And perhaps the best health advice is not to obsess about the latest demon nutrient, but to prepare whole foods for ourselves, adapting the old adage: everything in moderation, especially ultra-processed foods.