Evolutionary Medicine: why low-fat diets are bad for you
Nutrition is more dogma than fact
Every year our Nation’s TV Producer’s respond to the New Year by churning out a fest of diet programmes. The first episode of Channel 5’s New Year programme ‘Diet Secrets & How To Lose Weight’ was so bad it should never have been aired. Almost everyone of the so called ‘diet’ or ‘nutritional’ pundits made glaring errors by sprouting forth dogma that should have been purged from their collective psyche years ago.
Dogma: ‘Obesity is simply an imbalance between calories consumed and expended in the form of exercise’
It is now well known that not all calories are made equal in the context of human biology. Adipose or fat tissue is an organ that is controlled by a complex array of hormones and neuronal signals. Insulin is the master regulator that stores excess calories in adipose tissue. If you want to prevent adipose tissue forming you need to keep your insulin levels low, very low. How do you do this? In short you need to limit the amount of carbohydrates, or sugars, you eat. Glucose and fructose are the smallest building blocks of the sugars we consume in our diets. The higher your blood glucose and fructose levels go the more insulin your body produces and hence more of the calories you consume will be converted into fat. In comparison, proteins and fats don’t increase insulin levels and hence don’t stimulate the metabolic programme that drives adiposity (fat storage).
This is why high-fat (e.g. Banting) and high-protein (e.g. Atkins) diets are so effective in causing weight loss. Both these diets keep your insulin levels low and deplete your body of glycogen. Glycogen is the way your liver and muscles store carbohydrates. When your blood levels of glucose drop it triggers a process that results in your liver releasing glucose from its glycogen stores. The stores of glycogen are quite limited and when they run out your body turns on two other metabolic programs. One program is called gluconeogenesis; this is when your body start breaking down protein and converting it glucose. The second process is called ketosis; ketosis is the metabolic programme that mobilises fats, typically from adipose tissue, or from dietary fat and converts the mobilised fat to ketones. Ketones are then used by the brain, and the body, as an alternative energy source to glucose.
Please note that if your are on a high-fat, high-protein, low-carbohydrate (<50g of net carbohydrates per day*) diet the calories your consume will not raise insulin levels and hence you won’t put on weight. In fact, you will lose weight because ketosis rapidly mobilise fats from your adipose tissue. The problem with ketogenic diets is that you really need to keep the amount of carbohydrates you consume very low. If you don’t the carbohydrates you eat will raise your insulin levels and you then flip-and-flop between a state of ketosis and non-ketosis. In the non-ketotic state your body will store the excess calories provided by the high-fat diet as adipose tissue and your weight will stay steady. In the Channel 5 programme the celebrity on the ketogenic diet was doing just this; she was flip-flopping between ketogenesis and non-ketogenesis and hence she didn’t lose weight. It is clear that she was not sticking to the low carbohydrate aspect of the diet, i.e. she was almost certainly cheating by consuming to many carbs.
- * please note the amount of carbohydrates you are allowed to eat on a low-carb diet will vary from individual to individual, which is why nutritionists often advise using urine dipsticks or exhalation devices to monitor ketosis and to adjust your carbohydrate intake accordingly.
Another important aspect of the high-fat and high-protein diets is that they don’t generally restrict the number of calories you consume. Why? Firstly, by eating a enough calories in the form of protein prevents gluconeogenesis and hence it protects your lean muscle mass. The celebrity in the Channel 5 programme lost muscle mass at the end of the 4-week diet period. This occurred because she was not consuming enough protein in her diet and she was probably restricting her caloric intake. The latter would have triggered gluconeogenesis to maintain glucose levels until ketosis had developed. Please note ketosis takes time to kick-in, anything from 2 to 7 days, during which time gluconeogenesis has to provide energy for the brain. Therefore, flip-floppers tend to lose more muscle mass than dieters who maintain ketosis over prolonged periods of time. Another aspect of ketogenic diets is that before your brain switches into its ketone utilisation mode it has to rely on a dwindling supply of glucose that is being provide by gluconeogenesis. During the crossover period from gluconeogenesis to ketosis you don’t feel very well; i.e. you feel tired and lethargic, you find exercise hard and you may develop a headache. However, once you become ketotic these symptoms resolve and you start to feel normal; in fact some people report feeling supernormal when ketotic. Euphoria and a mild sense of being intoxicated is well described effect of ketosis. I suspect the latter is why there are so many ketosis addicts out there; they crave the sense of well-being that comes with being ketotic.
Most people ask ‘How can anyone lose weight on a ketogenic high-fat high-protein diet when I am consuming so many calories?’. The reason is the body has built in homeostatic (balance) mechanisms to control caloric intake. Fats and proteins are particularly effective at triggering the hormonal response that induces satiety, i.e. the feeling of fullness you get after a meal. In comparison, carbohydrates are very poor at inducing satiety, which is why people on a low-fat high-carbohydrate diet always feel hungry. People on a high-fat high-protein diet are not continuously hungry and don’t spend their day thinking of food.
Another positive effect of ketogenic diets is that ketones affect the brain in other positive ways and are anorexigenic (reduce appetite). Ketosis triggers complex hormonal changes in the body that reduce appetite. Contrary to what people expect caloric intake on high-fat high-protein diets actually drop spontaneously and people don’t overeat. This rule however only holds true if you are ketotic. As soon as you eat carbohydrates, and switch-off ketosis, your appetite comes back with a vengeance and your overeat to compensate for the adipose tissue you have just lost. From an evolutionary perspective people with lots of adipose tissue were protected in times of famine. This is why when carbohydrates became available to our ancestors, e.g. seasonal fruits, nuts and honey, they were endowed with the metabolic programme to store the excess calories as fat and to not switch off their appetites when eating carbohydrates; the so called gorging response. The fact that most modern societies don’t live a seasonal life, i.e. we now have access to a high carbohydrate diet all year around, partially explains why obesity has reached such epidemic proportions.
It is quite clear from archaeological and historical studies that our ancestors lived on a high-fat high-protein and a low carbohydrate diet most of the year. Our ancestors were seasonal eaters and hence only switched to a high-carbohydrate diet at specific time of the year when fruits, nuts and vegetables were in abundance. What is important to note from the above is that our bodies, or metabolism, has been optimised by evolution to use the time of plenty (late summer and autumn) to store as much of the calories consumed as carbohydrates as fat. In comparison, when carbohydrates were scare our ancestor’s metabolism was optimised to survive on a high-fat high-protein diet provided by animals (man is firstly a carnivore and only secondly an omnivore). Contrary to what many nutritionists say, from an evolutionary perspective a high-fat high-protein diet is very healthy. In comparison, a low-fat high-carbohydrate diet is the outlier; a continous high-carbohydrate diet is unnatural from an evolutionary perspective and is one of the reasons behind our obesity epidemic.
Evolution has not made all calories equal when it comes to adiposity. Calories consumed as carbohydrates, or in the presence of carbohydrates, are more likely to be stored as fat because of high insulin levels (hyperinsulinemia). Calories consumed as fat, in the relative absence of carbohydrates and insulin, will be converted to energy in the form of ketones. The high protein consumption that occurs in parallel with fat is used by our bodies to maintain our organs, in particular our muscle mass.
In conclusion, don’t believe everything you hear and see on television.
Please note this post is part of a series on evolutionary medicine and when I get the time I will try and slay many more nutritional dogmas.
Happy New Year. I hope it is a healthy one.