There has been a slow change in thinking by many nutrition ‘experts’ over the last few years. For so long it has been advised that carbohydrates should form the basis of our diets and that fat (particularly saturated fats) should be limited. This notion has been challenged by a number of high profile experts who are now advising that we eat high fat, or ketogenic, diets. What has since been started is almost a “black and white”, “us vs them” battlefield between advocates and opponents to high fat diets.
The Cholesterol Theory
One of the reasons why low fat diets have long been supported is based on the theory that high fat diets (particularly high in saturated fats) leads to increases in cholesterol, which in turn leads to increased risk of cardiovascular disease. There are a number of countries throughout the world though that go against this theory. Here in the U.K. we only need to look across to our French neighbors and look at what has become known as the French paradox  – even though, nationally, there is a high intake of dietary cholesterol and saturated fat, there are low rates of coronary heart disease. This appears to go completely against the cholesterol theory, although other factors may be playing a part such as levels of physical activity etc.
Proponents of high fat diets argue that it is higher levels of insulin – not cholesterol – that is the main cause of cardiovascular and metabolic diseases. This has lead to a number of studies (and personal anecdotes) showing that embarking on a high fat diet can result in weight loss and improvements in blood glucose levels and insulin sensitivity. These high fat diets promote eating more meat, fish, eggs and other foods high in natural fats such as avocados and coconuts while at the same time reducing amounts of (or completely eliminating) grains, fruits, starchy vegetables like potatoes, rice and any food high in sugar such as sweets and cakes. The diet contains a lot of animal products, and also advocates eating plenty of fibrous vegetables such as broccoli and spinach that are lower in carbohydrates.
One thing that high fat diet supporters do urge though is that this is not a ‘diet’ but a lifestyle – a point that may be missed by some. One of the biggest and highest profile proponents of high fat diets, Dr Tim Noakes has been quoted as saying that it is not a quick fix and that weight loss will be reverted if you go back to old eating habits.
There have been many arguments about the safety of high fat diets and one thing that has been made clear by such experts as Dr Noakes is that a high fat diet is “all or nothing” and that following a high-fat diet to lose weight, but cheating with the odd carbohydrate or a glass of wine could be harmful to our health.
The bottom line
There are many short-term studies that both support and refute the high-fat diet for health and weight loss. However, as of yet there is little evidence about the effects of high-fat diets compared to other diets such as higher carbohydrate. A review paper  from last year looking at published studies found that in longer-terms of weight loss:
● It is the reduction in energy intake in a diet that produces weight loss in overweight and obese people.
● The weight loss experienced by individuals is the result of the reduced energy intake, no matter how the proteins, fats and carbs are arranged in the diet.
● Because the longest follow-up in weight loss studies is 2 years, it is difficult to predict what the long-term effect of either diet will be.
However, this review only looked at prescribed diets that were matched for energy. In real life, most people will choose their own food and how much to eat and supporters of high-fat diets argue that people will naturally choose to eat less when eating a high fat diet (although this has again been debated).
One thing that both sides of the argument seem to agree on is that cutting down on the amount of sugar, processed foods and refined carbohydrates is important. Regardless of whether the diet is high in fat, carbohydrate or protein, the diets of those who live longest are often made from ‘whole foods’ and less from manufactured foods. If you are thinking about starting a high fat diet then it is important to get a health check first and consult a professional.
 Ferrières, J. (2004). The French paradox: lessons for other countries. Heart, 90(1), 107-111.
 Naude CE, Schoonees A, Senekal M, Young T, Garner P, Volmink J. Low Carbohydrate versus Isoenergetic Balanced Diets for Reducing Weight and Cardiovascular Risk: A Systematic Review and Meta-Analysis. PLoS One. 2014 Jul 9;9(7):e100652