There is a whole industry telling people what to eat, and frequently selling the dubious benefits (from diet books, to health food). It seems to me that most of it boils down to some simple rules that are easy to follow, and some points of controversy (on which it may not be possible to decide what is best). I follow a simple rules that work very well.
Of course, most of this assumes that you are a healthy adult: many medical conditions need special diets, and children’s needs are different from adults.
- Sugar is bad and should be consumed in much smaller quantities than is typical of modern eating habits.
- Fruits and vegetables are generally good (but see below for exceptions)
- Oily fish is good
- Transfats (heavily used in processed food) are bad, or at least possibly bad with no benefits
Generally agreed with caveats
- Whole grains are better than refined. Paleolithic and low carb diet advocates would say you should either eat little or now grain derived foods (after all human beings never evolved to eat grasses), or to eat only fermented grains. They also claim whole grains contain more anti-nutrients (mild/small quantities of toxins) than refined.
- Less processed it usually better.
- Some fats are better than others . Things generally agreed to be better include olive oil. Most medical opinion favours monounsaturated or polyunsaturated over saturated. Paleo diet would favour oil in food that you can eat raw, or can extract without heavy machinery (e.g. olive oil, coconut oil and, most of all, meat).
- Proportion of calories from fat vs carbs vs protein. Some low carb diet advocates promote high protein. Most medical opinion says high carb with less than 20% fat. Some low fat diet advocates say less than 10% fat. Paleo diet says high fat and low carb.
- Animal vs vegetable fat: conventional wisdom is that vegetable fat is better, paleo that animal fat is better as it is what our ancestors evolved to eat.
- High carb vegetables: obviously farinaceous ones such as potatoes, but also others such as many beans.
- Vegetables that cannot be eaten raw: discouraged on a paleo diet.
- Fatty dairy products: mostly low carb (unless sugar has been added), not paleo.
- Low fat dairy products: higher proportion of the calories in skimmed milk come from sugar: the fat would be preferable in a low carb diet.
Evidence and arguments
Medical research does not have a great track record on telling us what it is healthy to eat. Medical opinion has changed radically over the last few decades, sometimes more than once (eggs went from being regarded has healthy, to being considered a high cholesterol heart disease risk, and are now considered good again as dietary cholesterol is not generally regarded as a problem for healthy people).
Some logic also seems to be missing from many medical arguments. Consider that weight loss is encouraged by avoiding fat because fats have a high energy density (i.e. more calories per gram than other foods). That assumes that people eat a fixed weight of food, whereas different foods are not equally filling per unit weight. Why are Chinese meals (at least as served in the West) proverbial for leaving you feeling hungry an hour afterwards? That is because you need to eat a lot of a meal heavy in white rice to feel full for long: something that is also evident in modern South Asian eating habits that are based in large servings of white rice. We actually end up eating fewer calories on high fat diets.
There is also a lack of evidence on very important questions. Take a look at this summary of the evidence on the link between fat and heart disease, by the Cochrane Collaboration, a highly respected medical research non-profit organisation, best known for producing such reviews. There replacing saturated fat with monounsaturated or polyunsaturated may reduce the risk of heart disease, while there are no clear health benefits to reducing the total amount of fat we eat. This is critical given that reducing fat has been the most common medical advice on diet for the last few decades.
This is not surprising. The effects of diet are very hard to research. There are many bother factors (exercise, income, lifestyle), the effect of which are very hard to separate as they are highly correlated with diet and with each other. Long term studies are expensive. It is very difficult to accurately monitor what people eat.
The arguments can get very convoluted. For example, a low proportion of carbs compared to a typical diet can be achieved by eating lots of some types of fast food: but this a very different diet from what low carb diet advocates, or paleo diet advocates, recommend: it still has a much higher proportion of carbs, and a very different mix of fats.
A lot of the actual evidence in favour of a paleo diet is very well summarised by this post, which I will not duplicated here. There is more in favour of low carb diets in general in Gary Taubes’ book “Good Calories, Bad Calories”.
However, there is a more fundamental point in favour of the paleo diet in particular. Where the evidence is weak and lacking, the common sense starting point is what we evolved to eat. If I had to feed a lion, I would have no idea what specific nutrients it needed, but I know that wild lions live on raw meat, so that would be the obviously be a suitable diet. Similarly, in the absence of proof, the common-sense diet for humans is what wild humans (hunter gatherers) eat: meat, raw vegetables, etc.
What works for me
I am short so my weight for the last few years, of around 80kg, was already enough to make me fat (although not really obese). A holiday last November meant lots of eating out, and sent my weight up to 84 kg. Since then, I have managed to lose a steady kilo or thereabouts every month, with neither a great effort, nor calories restriction, nor an increase in exercise, and am now down to 76kg and my waist (measured in terms of which trousers fit) has shrunk significantly.
I have adopted what is best described as a paleo influenced diet. I keep the amount of carbs I eat, especially grains, low. However I am not very strict about it, and eat a moderate amount of non-paleo vegetables such as pulses I also drink as much full fat milk and non-sweetened dairy products as I want. I cook with copious amounts of ghee, olive oil and coconut oil. I do not even attempt to stick to my diet when I go out. I make no attempt to restrict the quantities I eat: I eat until I am full.
I disagree with the paleo objection to dairy, as it is evident that those of us with ancestors from parts of the world where milk has been drunk for a long time (Europe and South Asia) have evolved to cope with dairy: over 90% us have the gene that enables us to digest lactose as adults. I also do not see that milk is greatly different from other animal foods. I also do not believe that a strict diet is necessary. Humans are, naturally, opportunistic omnivores, like baboons. It is perfectly natural for us to have a a bit of everything, and we evolved to cope with this.
I am sure that it would be better to also follow the palaeolithic lifestyle in terms of exercise: regular light exercise such as walking, with short bursts of activity such as running. I get very little exercise, and my plans to change that are rather like St Augustine’s prayer for chastity “but not yet”.