Doctors on the low carb bandwagon

There’s a movement in medical circles towards a low carb, high fat diet for the treatment of diabetes and obesity – a main topic in last month’s Journal of the American Medical Association. It is extending into the idea that this diet is what we should all be eating all the time. We can also see this in the plethora of recent doctor-led TV series with a leaning in this direction.


Of course, on the one hand, it is great news that more doctors are singing an anti-sugar mantra, however many advocates shun all supplements and don’t seem at all concerned about driving people into a diet with lots of meat, animal fats and dairy products, despite possible long-term harm. Fruit is also being demonised despite virtually every study showing the more fruit eaten the healthier and longer a person lives. It is certainly not vegan friendly.

The movement generally looks simply at controlling amount of carbs with very little awareness that not all carbs are created equal. The existence of a measure of a carbohydrate’s effect on blood sugar, and hence insulin release, which all agree is the key parameter you want to bring down, namely the Glycemic Load or GL of a food, seems to have not yet hit the radar.

 Good evidence?

There are enough studies now to know that this low carb, high fat approach is more effective than the ‘old school’ low fat, high carb calorie controlled diet for reversing diabetes and losing weight. A meta-analysis of 13 randomized controlled trials suggests that people on ketogenic diets tend to lose more weight and keep more of it off than people on low-fat diets.In a recent 8-week randomized trial including 34 obese men and women, those who ate a ketogenic diet lost 9.7% of their body fat, while those on a low-fat diet lost just 2.1%. It’s also good for diabetes (type 2). A GP from Southport, Dr David Unwin offered this kind of diet to his patients and a quarter reversed their diabetes.

While a low carb, high fat diet works better than a low fat diet there’s no good evidence that it works better than a controlled low GL diet or a diet that just avoids all sugar. Comparison studies just haven’t been done.

A Tale of Two Fuels

We are designed to be able to derive energy from two fuels –glucose, the breakdown product of carbohydrates and ketones, the breakdown products from fats.

If given the choice our cell’s energy factories, mitochondria, choose glucose. When there is excess glucose it is put into storage as fat. An indicator of ‘too much’ intake of glucose/carbs is an increase in blood fats, triglycerides.

Alternatively, we can convert fat in the liver, and most easily what are called ‘Medium Chain Triglycerides’, into ketones and use them as an alternative fuel for the mitochondria. Coconut oil is an example of a fat that is predominantly MCTs.

Having two sources of potential fuel – fat or carbs – has many evolutionary advantages. If we were to run out of carbs or food the bodycan switch to eating fat or burning its own fat reserves. The heart has a supply of fats around it, which give it an immediate back-up system were glucose to run out.

So, why force a switch to burning ketones? Well, large chunks of humanity have become, not only sick from the effects of eating too many carbs, but also addicted. This creates insulin resistance, and healthy insulin function is vital for clean delivery of glucose into cells. As a consequence our ‘sugar metabolism’ machinery is knackered. Switching to that largely unused ‘ketone engine’, under these circumstances, is a welcome break.

One concern is that ketogenic diets tend to be based on lots of meat and dairy (and many people on Atkin’s-like diets do eat meat twice a day, which stresses the kidneys) could reasonably be expected to increase colo-rectal cancer risk in the long-term. This is due to the well established presence of three carcinogens in cooked red and processed meat – PCAs, HCAs and heme iron. Constipation, or slow gastric transit time, also means that these carcinogens are present in the gut for longer. In addition, high dairy and meat dietspromote insulin-like growth factor (IGF-1), which makes cancer cells grow faster. In my opinion IGF-1 should be being monitored in trials of low carb, high fat diets but it rarely is. The counter argument is that insulin levels drop on a high fat low carb diet, which is itself anti-cancer. We just don’t have long-term studies yet to know the answer. Of course, you can avoid this potential risk by eating a fish-based or more vegan ketogenic diet – or going ‘Fishkins’.