Power: Fasting vs Low Carb – Fasting 26

By Jason Fung, MD

What’s the difference in power between fasting and Low Carb High Fat (LCHF)? Sometimes it feels like arguing whether Batman or Superman is more powerful (Superman, of course). But they’re both superheroes, and the point of both these dietary superhero regimens is to lower insulin. This stems from a rational examination about the causes of obesity and type 2 diabetes. You need to understand the aetiology of obesity (the underlying cause) if you are to have any hope of treating it.

For decades, we have laboured under the false assumption that excessive calories caused obesity. However, overfeeding and underfeeding studies clearly proved this hypothesis wrong. If calories caused obesity, then overfeeding calories should cause obesity. It did, but only in the short term. Long term, weight went back to normal. Underfeeding calories on the other hand, should lead to permanent weight loss. But it did not. The failure rate of this Caloric Reduction as Primary strategy is an abysmal 99%.

Using a more rational model of obesity as a hormonal disorder (mainly insulin, but also cortisol) leads to the hypothesis that increasing insulin should lead to lasting weight gain. Decreasing insulin should lead to weight loss. And guess what? It worked just as advertised. (See the Hormonal Obesity series for a full description).

So, if we understand that excessive insulin causes weight gain, then the treatment is quite clear and just really damned obvious. You don’t need to decrease calories, although there is some overlap. You need to decrease insulin to cause weight loss. Both LCHF diets and fasting accomplish this goal. Refined carbohydrates are the biggest stimulus to insulin, so reducing carbs reduces insulin. Protein, especially animal proteins also raise insulin, so keeping protein moderate and fats high is another way to keep insulin levels down. Fasting, by restricting everything, also keeps insulin down. A ‘fat fast’ ie. eating nothing except pure fat, may also accomplish the same thing, but studies are sparse. So ‘bulletproof coffee’ may certainly achieve the same goal of lowering insulin without lowering calories, but the data are simply no there to say for certain.

But which diet is better? LCHF or Fasting? A comparison of power shows that fasting wins every time. In this study of a carbohydrate free diet vs fasting in type 2 diabetics, you can see that carb-free does extremely well. If we compare the glucose response of Carb Free versus a Standard Diet, you can see that blood sugars come way down. But fasting does even better.

If you are trying to lower blood glucose, nothing really beats fasting. After all, you can’t go lower than zero. Even then, the carb-free diet does remarkably well – giving you 71% of the benefits of the fasting, without actual fasting. The standard diet was 55% carbohydrate and 15% protein, and 30% fat – not far off of what most dieticians and Dietary Guidelines recommend. You can see how shitty it is for actual blood glucose control.

The carb-free diet is <3% carbs (that is ketogenic or ultra-low carb), 15% protein (moderate)  and 82% fat. LCHF pretty much says it all. The calories delivered were 25 kcal/kg (1750 calories for a 70 kg man) in 3 meals – this was the same between the standard and carb-free diets. So the benefits of carb restriction on blood glucose were NOT simply due to calorie restriction. This is useful knowledge, considering how many ill informed idiots doctors and dieticians keep saying ‘It’s all about the calories’. Actually, in this study, it had nothing at all to do with the calories.

Anybody who still believes that ‘It’s all about the calories’ despite 50 years of unrelenting failure of the Caloric Reduction as Primary (CRaP) model either has not thought about things very hard or is simply not all that intelligent. Yes. If a strategy such as CRaP fails for 50 years, we should be changing our strategy. It doesn’t take Albert Einstein to tell us that is the very definition of insane.

This graph is pretty sobering. Looking at the Standard Diet (ADA recommended), you can see how high those peaks of glucose really get. You might rightfully ask yourself, if the good folks at the ADA knows that their diet sends blood sugars skyrocketing upwards, why on earth would they recommend it? Are they trying to kill us? Unfortunately, the answer is yes. They are trying to kill you. Not intentionally, but with their ignorance. All that money showered upon them from Big Food and Big Pharma have something to do with it, too.

But what is carb-free just isn’t enough? I have lots of patients who limit their carbohydrates but still have elevated blood sugars. How do you get more power? Sorry, Batman, it’s time to call in Superman. (Don’t bother about the Wonder Twins – they were always useless. One of them would turn into a dolphin or something.) In a word, we need Fasting.

The study results are even more impressive when you look at insulin levels. This is very important because blood glucose levels are not the main driver of obesity and diabetes. Insulin is the main driver. The entire strategy of weight loss hinges upon lowering insulin.

Looking at total area under the curve, you can see that carb free diet can reduce insulin by roughly 50% but you can go another 50% by fasting. That’s power.
This makes sense, of course. A carb free diet will still contain some protein which will increase insulin. The only way to get lower would be to eat 100% fat – which is largely an artificial construct. That is, we don’t generally eat pure olive oil as a meal or pure lard. Bulletproof coffee is certainly a great ‘hack’ but it’s hardly been tested by thousands of years of human history and millions of people. Fasting has survived this test of time. It is Anti-Fragile. How? The more we eat processed and ultra-processed garbage and pretend it is food, the more we need to fast. If you eat a lot of fast food (foods that are ultra-processed and send insulin skyrocketing) the more you need to fast (bring those insulin levels back down).

And NOTHING beats fasting for bringing down insulin. It is simply the fastest and most efficient method of reducing insulin. Luckily, it’s also not as hard as most people believe it to be.

What about glucagon? Remember that glucagon is sort of the opposite of insulin. One of insulin’s main physiologic role is to suppress glucagon. Dr Roger Unger did much to explore the biological role of glucagon and often considered it the most important. However, in this study, it had no clinical relevance at all. In dealing with patients, glucagon also plays little or no role.

Let me explain. Insulin causes weight gain – so giving insulin causes weight gain. Does reducing glucagon cause weight gain? Not really. Does increasing glucagon cause weight loss? Not really. Sure, glucagon plays a primary role in rat livers, but I don’t really care. I care about humans.
The bottom line of this study is to reinforce what we knew already. Insulin is the primary (but not the only) driver of obesity. Therefore, for most people, reducing insulin is the best method of treating obesity. Carb free diets are a powerful method of reducing insulin. But if that doesn’t work, then intermittent fasting offers an even more powerful strategy.

In type 2 diabetes, you can reduce blood sugars by 50-70% by carb free diets. You can reduce it another 30% with fasting. So, if we already know how to reduce blood sugars in T2D with dietary strategies – why do we need medications at all? Here’s the answer, of course. You don’t. Type 2 Diabetes is an entirely reversible disease.

Start here with Fasting part 1

Continue to Fasting Part 27 – The difference between calorie restriction and fasting

By The Fasting Method

For many health reasons, losing weight is important. It can improve your blood sugars, blood pressure and metabolic health, lowering your risk of heart disease, stroke and cancer. But it’s not easy. That’s where we can help.

Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

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