Human energy comes mainly from two macronutrients – carbohydrates and fat. A ketogenic diet relies almost exclusively on fat as the primary source of fuel, so it’s probably important that you understand what fat is, what kinds of fats to eat and where to find them. Become a fat connoisseur!
Saturated and monounsaturated faty acids for fuel
Aim to make up the bulk of your fat intake from saturated and monounsaturated fats. These are our main fuel sources. Eat as much as you like (within your energy needs!)
Polyunsaturated faty acids (PUFA) and Essential faty acids (EFA)
Try to limit your intake of PUFA to less than 5% of your overall calories, and try to get a fairly equal mix of omega-3 and omega-6. The marketing people will tell you to eat plenty of these.
However, ketogenic diets consist mainly of fat, which will ensure you are consuming enough PUFA (including essential ones), because there are small amounts in most foods. In fact, on a ketogenic diet, one should view PUFA and essential fatty acids as vitamins, and should not go out of your way to consume them in any quantity, particularly omega-6.
Fats to cook with and fats for dressings
All cooking fats eventually break down and oxidise under heat, which is undesirable for health reasons. Saturated and monounsaturated fats are more robust and will withstand higher cooking temperatures. The golden rule is to cook and fry with high saturated/monounsaturated fats, and make dressings/toppings with oils containing more polyunsaturated fats (being careful not to consume too much PUFA or omega-6)
In any case, it’s best to avoid oils with a high omega-6 to omega-3 ratio like safflower oil, sunflower oil, cottonseed oil, corn oil, sesame oil, and soya oil.
Here the data is far less clear cut. The sources of foods can have a huge impact on the balance of omega-3 to omega-6 (also referred to as n-3 and n-6), and as we know the ratio of omega-6 to omega-3 is quite important for health. It’s very difficult to find any consistency in reports of essential fatty acid contents of common foods (I doubt such a list exists). However, by looking at a number of sources, we can begin to discern patterns.
Oily Fish : here is one source of data on the essential fatty acid content of common foods. If you look at the atlantic salmon and add up the n-3 (another term for omega-3) acids, you will find it adds up to 2018mg/100g of product and n-6 add up to 439mg/100g. This provides an n-6:n-3 ratio of around 1:4 which is outstanding – but if you look here you will find Salmon, cold water, fresh and frozen, cooked listed at 1.7g/113g of n-3 which is 1504mg/100g of product and about 30mg/100g of n-6 – an n-6:n-3 ratio of 1:50 (quite different from 1:4). However, in both cases the data indicates a good or excellent n-6:n-3 ratio.
Beef : looking at the first source of data above, we see that sirloin steak has 103mg/100g n-6 and 50mg/100g of n-3. That is to say, an n-6:n-3 ratio of around 2:1. However, looking here it still have a similar ratio of n-6:n-3, but the absolute quantities are 300mg/100g n-6 and 152mg/100g n-3 – three times higher. However, the n-6:n-3 ratio is acceptable.
Pork : from this source we see an n-6 content of 315mg/100g and an n-3 content of 24mg/100g – a ratio of 13:1 – clearly not good. Looking at this alternate source we see n-6 at 370mg/100g and n-3 at 20/100mg – an n-6:n3 ratio of just above 18:1. It’s probably fair to say that pork is probably best left alone or severely restricted.
Chicken breast (without skin) : from this source we see an n-6 content of 650mg/100g and an n-3 content of 80mg/100g – a ratio of 8:1. Don’t even consider eating the skin – it’s insanely full of n-6. Now if we look here we see 170mg/100g n-6 and 40mg/100g n-3 – a ratio of 4:1.
Clearly, this is not healthy territory for anyone with obsessive compulsive tendencies. Despite the broad variation in data a pattern does arise which suggests one should consume more oily fish, and less land animal meat.