The impact of a 10% limit on saturated fat – Zoe Harcombe email

The impact of a 10% limit on saturated fat

Executive summary

This is a short note with a big finding.


I know someone who was diagnosed with pre-diabetes and he avoided becoming a type 2 diabetic by adopting a very low carbohydrate diet. He committed to consuming less than 10% of his diet in the form of carbohydrate. To achieve this, he decided that he would avoid all foods containing more than 10% carbohydrate and then he would never exceed the 10% limit in his overall diet. I thought that was a clever way of executing his plan.

It made me think of the saturated fat guideline that has been in place since 1977 in the US (and adopted in other countries since): “Thou shall have no more than 10% of one’s calories in the form of saturated fat.” Notwithstanding that this guideline has no evidence base, if one followed the above principle of achieving this restriction by not eating any single food with more than 10% saturated fat, what would one be able to eat?

The facts about fat

Before we answer that question, we need a quick recap on the facts about fat, which I cover in many of my conference presentations. The three key facts are:

1) All foods that contain fat contain all three fats – saturated, monounsaturated, and polyunsaturated – there are no exceptions.

2) The only food that doesn’t contain even a trace of fat is sugar. Even lettuce and blueberries have a trace of fat although they can be treated as fat free. If foods have even a trace of fat, they have a trace of saturated fat – see point 1.

3) If we define food groups as meat, fish, eggs, dairy products, nuts & seeds, legumes, grains, vegetables, and fruits, then dairy products are the only food group that contains more saturated than unsaturated fat. Not that saturated fat is bad and unsaturated fat is good, but just to state a fact about fat. Some individual foods (e.g. coconut) have more saturated than unsaturated fat, but only one food group has this characteristic.

The 10% rule

When dietary guidelines say, “no more than 30% total fat” and “no more than 10% saturated fat”, what they mean is – as a percentage of one’s daily calorie intake. Applying this to any one food means that overall calorie intakes don’t need to be counted, which makes life easier.

Individual foods can be analysed on the basis of weight or energy (calories). Using 100 grams or 100 calories is ideal, as the use of 100 gives us percentages automatically.

Let’s take a standard apple from the US all-foods database (Refs at end for all foods). The all-foods database uses weight as the primary measure, rather than calories. Per 100g, a standard apple has 52 calories, of which 49.7 are from carbohydrate, 1.4 are from fat (lol!) and 0.9 are from protein. We can see that an apple would fail our friend’s 10% carbohydrate rule, since 96% of the calories come from carbohydrate, However, this would pass the saturated fat test, because only 2.7% of the total calories come from fat, so saturated fat would be an even smaller part of that 2.7%.

Foods that pass and fail the 10% saturated fat test

I analysed a number of foods from the US database and categorised them as real vs processed foods and those meeting the 10% saturated fat guideline or not. I chose foods to establish likely outcomes for whole food groups. For example, I analysed a lean steak and this failed, so red meat generally is likely to fail. (Please remember that this is just a guide – someone could have steak and chips and the whole meal may end up under 10% saturated fat because the chips might lower the average, but it’s a really useful guide to see what would be ‘best avoided’ to meet a 10% saturated fat target.)

These were the findings (red = fail and green = pass):

Please note that some muffins, cakes, doughnuts, biscuits will fail the 10% saturated fat test, but the first (standard) examples I tried in each of these categories passed.

The foods analysed

I’ve included the reference for each food and extracted the following – all per 100g of food item:

i) The grams of saturated fat;

ii) The calories for these grams (grams multiplied by 9);

iii) Total calories for 100g of the food;

iv) The calculation of saturated fat calories as a % of total calories (ii over iii)

You can see that eggs and dairy will always fail – if low fat milk fails, all dairy fails. Olive oil interestingly fails. Normal ice cream fails (it’s dairy); fat free ice cream (which is basically sugar) passes. That leads to another observation – the sugar content in some of the foods that passed was as high as 39% (e.g. frosted rice crispies).

The finding

There’s a quotation attributed to Einstein along the lines of “If we knew what it was we were doing, it would not be called research, would it?” Quite often I start something and have no idea where it is going to end up. This bit of research – inspired by someone’s approach to their own health – ended up with a striking observation…

The Scientific Report for the 2020-2025 Dietary Guidelines for Americans was published in July 2020 (Ref 2). This is the comprehensive document (835 pages), which precedes the Dietary Guidelines for Americans, which are due out any time now. The July report suggested that there would be no lifting of the 10% cap on saturated fat – indeed one committee member wondered why the saturated fat intake couldn’t be zero! (A committee member who clearly did not know the basic facts about fat).

As we await the final guidelines, it is difficult to think of a dietary guideline that would be more effective in driving people away from animal foods than the 10% saturated fat restriction. Not because animal foods are high in saturated fat – remember only dairy as a food group has more saturated than unsaturated fat – meat, fish and eggs all have more unsaturated than saturated fat. But because, even with a 2% saturated fat content in steak (by weight), this ends up being more than 12% of calories in the form of saturated fat.

The introduction and retention of the 10% saturated fat cap is the single best way to mandate a plant-based diet. Now that we know this, it makes more sense, because it never made any sense from an evidence perspective.

Until next time

All the best – Zoë


The foods analysed:
Sirloin: Steak
Cheddar Cheese:
3.5% Milk:
1% milk:
Olive oil:
McDonald’s Ice cream:
McDonald’s Muffin:
Rapeseed oil:
Commercial bread:
Frosted rice crispies:
Kellogg’s low-fat granola:
Krispy Kreme doughnut:
Cake sponge commercial:
Kidney beans:
Skinless chicken breast:

Ref 2:

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