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How much fat to eat on a ketogenic diet - is fat free?


Is fat free?

In some pockets of the low carb community, there is the message that we should be eating high fat all the time, no matter what; fat is free, fat is fine, you can’t overdo fat. It is true that fat does not stimulate your insulin. However, extra added fat is not a great idea if weight loss and metabolic health are your goals.

Eating extra fat in the form of fat bombs and bulletproof coffee is wildly popular, but does it promote weight loss? Or does the extra fat make you fatter?

The answer is, as so often in biology, it depends.

It depends on your hormones, namely insulin and leptin.

If you are lean AND have no metabolic disease (that is no obesity/ fatty liver/PCOS/type 2 diabetes/insulin resistance) AND if you are on a low carb/ketogenic diet – then the extra fat you eat probably won’t make you fatter.

But if you are overweight then the extra fat could indeed cause added weight gain. At the very least it will slow down your weight loss. This has nothing to do with calories and everything to do with hormones.

Here’s a simple rundown of why fat bombs and bulletproof coffee are not the weight loss miracle they are marketed to be.

I’ll start with a super summary, then get down into the nitty-gritty for those who want to read on.



In lean people the hormonal regulation of weight gain is normal. If a lean person eats extra fat, they get fuller and compensate by eating less.

In overweight people, the hormonal regulation of weight gain is out of whack. If they eat extra fat, they don’t feel fuller and don’t compensate by eating less.



First, let’s get to know insulin and leptin:

Insulin is the main driver of weight gain; insulin tells the body to store fat. Leptin tells the body to stop storing fat. It does this by turning off hunger, making us stop eating for a while.

Insulin = the fat-storing hormone.

Leptin = the satiety (stop eating and stop storing fat) hormone.

They are opposites.


Normally, when our bodies aren’t hijacked by high-carb processed foods, insulin and leptin are in balance. This is why there were no obese cavemen. Their leptin didn’t let them get obese.

But the modern diet of high carb and processed foods hijacks this system, causes persistently high insulin, and then insulin resistance, which in turn causes persistently high leptin and eventually leptin resistance.

So, lean people are leptin-sensitive and obese people tend to be leptin-resistant.

Back to the fat bombs….

When we eat carbohydrates and protein it gets absorbed from the intestine to the liver and also stimulates insulin.

Fat is different.

When we eat fat, it gets absorbed from the intestine into the lymphatic system, then straight into the blood; no liver involved, no insulin stimulated.

The fat we eat goes straight into our fat stores.

If a lean person is eating heaps of extra fat, then as the body’s fat stores increase the leptin will increase. Because they are leptin sensitive their body will respond appropriately to the increased leptin, and they will naturally stop eating in order to let the body weight go down. A lean person eats extra fat, and their hunger goes down.

Now, if an obese, leptin-resistant person eats and drinks heaps of extra fat, that fat also goes straight to their body’s fat stores. And here’s the sticky bit – if you are leptin resistant (as most people with obesity and metabolic disease are) that dietary fat goes into the fat stores – leptin levels are raised but the body can’t respond, the body is deaf and blind to the elevated leptin. If an obese person eats extra fat, it goes into the fat stores, but hunger does NOT go down.


So, are fat bombs and bulletproof coffee bad? No!

They are fine for people on a low carb diet who are not obese, do not have any metabolic disease, and do not have a weight loss goal.

BUT if you do have a weight loss goal, or you have issues with obesity/insulin resistance/leptin resistance/fatty liver/PCOS/type 2 diabetes or metabolic syndrome, then extra added fat will prevent weight loss and could hamper your progress.

So, in conclusion, if you want to lose weight or heal your damaged metabolism then don’t drink your fat and don’t overdo the fat bomb snacks.

Instead, eat low carb real food.

Eat three meals a day (or less).

Eat whole food until you are full – veggies/nuts/seeds/meat/eggs/fish/seafood/some added fat for cooking.

Don’t snack and don’t drink your calories.

Add in intermittent fasting when you want.

What you don’t want to do is eat low carb real food until you are full, and then add in extra butter, oil, fat bombs, or high-fat snacks.

If you stick to whole foods, you can’t go wrong.

Eat a piece of chicken with the skin on. Don't fear the chicken skin!

But if weight loss is your goal, then best you don’t chase your chicken meal with a cup of flavoured coconut oil, buttered coffee, or a chocolate-coated fat bomb.

Fat is not dangerous, but nor is it a “free food”.

Eat low carb real food and you’ll be fine.

In health,

Dr Mary Barson


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