If there was anything I thought I knew when I was an insulin-fearing keto zealot, it was:
- the blood sugar roller coaster is bad, and
- stable blood sugars were good.
According to the keto gurus that I followed, if you wanted to lose fat and optimise your metabolic health, the most important thing you could do was eat fewer carbs to achieve flatline blood sugars to “turn off insulin”.
Even today, with the keto movement in decline, there is still plenty of confusion about the role of stable blood sugars, insulin and weight loss.
Many people assume that stable blood sugars will lead to lower insulin levels which will automatically lead to weight loss.
Since we started the Data-Driven Fasting Facebook Group, we’ve had a barrage of questions as people try to make sense of their blood sugars.
Since then, we’ve had thousands of people complete our Data-Driven Fasting Challenge.
Now, the data is in.
The data clearly shows that eating a high-fat diet to stabilise your blood sugar is unlikely to help you lose weight.
Rather than worrying about your blood glucose after meals, your blood glucose before meals is a much more powerful way to optimise your metabolic health.
By managing your blood sugars before you eat (through meal timing and optimised food choices), you can optimise the numbers that matter when it comes to managing your metabolic health (i.e. BMI, waist to height ratio and waking blood sugars).
Eighteen years ago, I married Monica, who has Type 1 Diabetes.
We started to think about having kids. But she knew she needed to get her blood sugars under control to minimise the long list of dire complications of pregnancy with high blood sugars.
She has lived with Type 1 Diabetes since she was ten years of age. But sadly, no endocrinologist or diabetes educator had ever been able to tell her what to eat or how to manage her insulin dosing to help her gain control of her diabetes.
The conversation always went along the lines of…
Endo: “Your blood sugars and HbA1c are high. You should try to get that down.”
Monica: “How doc? What do I do? What do I eat? What do I change?”
Endo: “It just needs to be better. Here’s your script for insulin and drugs. See you in six months.”
Luckily, when we were looking at having kids, we found a progressive doctor who taught us enough enable Monica to get reasonable control for our two pregnancies. Back then, we learned about matching carbohydrates to insulin dosing and how to fine-tune insulin sensitivity. Seventeen years later, they seem to have turned out OK.
Bernstein was an engineer who later became a doctor after he got frustrated at people not listening to his theories about diabetes management that he discovered after analysing his own blood sugars. He’s now 85 and going strong. He continues to walk the talk.
Recently, we had to see an endocrinologist and a diabetes educator get a new insulin pump for Monica so we could set up a closed-loop CGM/insulin delivery system. The conversation with both of them went along the lines of:
“Wow. What a fantastic HbA1c! I don’t think I can teach you anything! You know what you’re doing… But wait. Your chart says you haven’t seen an endocrinologist for seven years. What?!?!”
Over the past few months we have been able to use the closed loop CGM system, combined with wise dietary choices, to achieve even better blood sugar control.
And a non-diabetic HbA1c of 4.9%!
I have learned a lot after diving deep into the Type 1 Diabetes headspace. I also learned that context is critical, especially if you are part of the 98.5% of the population who has a functioning pancreas.
Before I get into the data analysis and learnings from people using Data-Driven Fasting, let me give some background to help you understand the difference between people with Type 1 Diabetes and the rest of us.
What we know from people with Type 1 diabetes
Injecting large doses of insulin to treat elevated blood sugars from modern processed food leaves them on a blood sugar rollercoaster. When their blood sugars are high, they inject more insulin to bring them down.
A few hours later, when they find they have overshot their blood sugar target. They are ravenously hungry and will eat anything and everything until they can raise their blood sugars again. A day in the life of most people living with Type 1 Diabetes looks like this.
Injected insulin is driving their appetite.
If their insulin doses are not precisely matched with the food they eat (which is nearly impossible with synthetic injected insulin combined with synthetic, processed food), they end up overeating because of the insulin they are injecting.
Living with rollercoaster blood sugars sux. Your appetite, mood or energy levels are in the toilet!
To be clear, whether you are injecting insulin or not, you don’t want to have wildly osciallating blood sugars. When they come crashing down below your normal baseline levels, you will feel super hungry and compelled to overeat.
People who are metabolically healthy tend to see their blood sugars rise by less than 1.6 mmol/L or 30 mg/dL after meals. So you ideally want to cut back on carbs (to avoid overfilling your glucose fuel tank) to achieve blood sugars in the normal healthy range.
However, swinging to the other extreme and simply replacing all carbohydrates with refined fat (and even avoiding protein) to achieve flatline blood sugars does not address the root cause of type 2 diabetes/metabolic syndrome/insulin toxicity. It’s largely just symptom management, not the cure.
How insulin really works
While we usually think of insulin as the hormone that forces energy into our cells, it’s not the full story.
While this is a compelling metaphor, suggesting that we will grow fatter just by eating carbs, irrespective of energy balance, it is incorrect and fundamentally misguided.
We all have approximately 5 grams of glucose (or 20 calories worth) buzzing around in our body at any one time (i.e. about a teaspoon’s worth). It doesn’t take long to use this up once we turn off the flow of energy into our bloodstream.
If you could turn off the release of energy from your liver completely, you would run out of glucose completely in about 15 minutes.
Insulin is the hormone, secreted by the pancreas, that reduces the flow of energy into your bloodstream (from your liver and adipose tissue) until you burn up the energy in your blood from that last meal.
As per Dr Bernstein’s Law of Small Numbers, once people with Type 1 Diabetes reduce the inputs that require larger doses of insulin (i.e. processed carbohydrates), they can stabilise their blood sugars and insulin requirements.
Smaller inputs of carbs and insulin with meals lead to smaller errors that are easier to correct throughout the day. Then, because they are no longer injecting excessive amounts of insulin to treat the blood sugar roller coaster, their appetite stabilises, and they tend to achieve healthy body fat levels.
Rather than rollercoaster blood sugars with poor appetite control (which drives an energy surplus), they can have stable blood sugars and healthy appetite signals. If you are part of the 1 in 8000 people with T1D whose pancreas doesn’t work, stabilising your blood sugars and insulin should be your #1 priority!
The difference between people with Type 1 Diabetes and everyone else!
But, if you are part of the 98.5% of the population that is fortunate enough to have a functioning pancreas, EVERYTHING IS DIFFERENT.
You cannot turn off your insulin pump or stop taking insulin.
No matter what we believe, it just doesn’t work like that!
Your pancreas will always produce just enough insulin (no more, no less) to hold your body fat in storage until you have used up the extra energy from the food that is coming in from your mouth.
When you stop eating, insulin levels lower and your stored energy is allowed to be released for use.
If you have Type 2 Diabetes and eat a heavily processed diet of carbs and fat (e.g. modern processed junk food) your blood sugars will shoot up after you eat and take a long time to reduce back to baseline.
But what if I’m “insulin resistant”?
Many people have developed a victim mentality (I was one of them).
They blame their obesity on their insulin resistance.
They think being insulin resistant makes it harder for them to lose weight.
But, the reverse is actually true.
When you are lean and insulin sensitive, your body is only too willing to store energy and grow. A starving caveman or a lean body builder after a show is highly insulin sensitive, ready to store every moresel they can get their hands on.
However, conversely, once you become insulin resistant, your body is only too willing to offload the excess energy as soon as you stop jamming in excess energy from low satiety nutrient-poor processed foods that are driving you to overeat them.
The chart below shows the difference between diabetic and healthy blood sugar levels (i.e. higher and with larger swings).
Foods that are a combination of fat+carb together enable your body to fill both fuel tanks at the same time. Because your fat stores are already full, the extra energy is not easily absorbed by your liver and body fat, so it overflows into your bloodstream.
You can’t blame getting fat on insulin. You’d die without it. You don’t really want to turn off your pancreas. Trust me – being an uncontrolled Type 1 Diabetic in ketoacidosis is not fun.
It’s the foods with carbs and the fat (with low protein) that caused you to overeat. Now you have lots of body fat that requires lots of insulin to hold in storage so long as you keep eating that food.
As you will see below, it’s not that stable blood sugars or a low carb diet is a bad thing. However, eating a high-fat diet to achieve stable blood sugars is largely symptom management.
Switching carbs for refined fat and avoiding protein won’t make you lean and metabolically healthy. It often makes things worse!
Is insulin REALLY the problem?
Over the past few years, people in the fasting/low carb/keto community have been told by doctors and nutrition gurus that insulin toxicity is the root cause of the majority of our western diseases.
Insulin is public enemy number one and reversing “insulin toxicity” is key to weight loss.
We don’t have a lot of data about our insulin response to the food we eat. But important to note that the data we do have (i.e. the Food Insulin Index data) only measures the response to foods over the first two hours (as shown in the chart below).
The limited duration of this data lead many people to think that high-fat foods have a negligible impact on insulin and hence they are effectively a “free food”.
While glucose will raise your insulin levels quickly, foods that contain fat and carbs together (like milk, shown by the aqua line) will have a smaller initial impact, but insulin will stay elevated well beyond two hours.
While we don’t know that much about the long term insulin effect of high-fat foods, it appears that they will keep our insulin levels elevated for longer. Because fat is stored more efficiently, you don’t need as much insulin to hold it in storage, on your bum and belly.
Your body wants to excess glucose quickly, so it raises insulin to abruptly halt the release of stored energy until you have burned it off. However, because your body can store massive amounts of fat there is no need to raise insulin as much. Your body is more than happy to store all the fat it can get for a possible famine.
Once we understand that insulin simply holds our stored energy back while we use up the energy coming in from our diet, we realise that ALL food will increase insulin over the long term. The problem is not insulin toxicity, but rather energy toxicity (that leads to increased insulin levels).
The bottom line: If we want to lose fat from our body, then it’s not merely a matter of eating fewer carbs and more fat.
Show me the science!
Since launching the Data-Driven Fasting Group, I have been bombarded with questions about blood sugars and insulin as people test their blood sugars and try to make sense of the data they see.
Why do my blood sugars rise when I don’t eat?
My blood sugars are flatline? Why am I still fat?
I thought it would be interesting to see what we could learn from this massive dataset.
The most important markers to manage
When it comes to metabolic health and longevity, there are three things we can easily measure that we collect in Data Driven Fasting:
- body mass index (BMI),
- waist to height ratio, and
- waking glucose.
As shown in the charts below of body mass index, waist:height ratio and waking glucose, lower is not always better. However, due to the constant availability of hyperpalatable nutrient-poor processed foods, most of us are well on the higher side of optimal.
Flatline CGM envy… Why are still chasing the wrong numbers?
These days, I’m seeing more and more people (who don’t have Type 1 Diabetes) walking around with (expensive and often painful) continuous glucose monitors eating more fat and less protein and less carbs to maintain flat line blood sugars.
They post their flat line blood sugars on Facebook and Instagram.
A few years ago it was ketone envy. Now it’s flatline CGM envy.
CGM technology is a Godsend for people (like my wife) who have Type 1 Daibetes and need to constantly keep an eye on their blood sugars. But, while everyone wants the latest gadget, for most people, more data is not better.
If you already have a CGM (or are considering purchasing one), you may be interested in checking out How to lose weight using a continuous glucose monitor (CGM).
How much should my blood sugars rise after a meal?
The table below shows the generally accepted limits for blood glucose after meals.
The key things to note here are:
- If your blood sugars after meals are elevated above 140 mg/dL or 7.8 mmol/L then you have prediabetes or diabetes and definitely need to work to reduce our post-meal blood glucose by reducing refined carbohydrates and/or medications to reduce blood sugars (e.g. insulin or metformin).
- A rise in glucose from 100 mg/dL to 140 mg/dL would be accepted as normal and healthy. If your blood sugars rise by less than 40 mg/dL or 2.6 mmol/L after meals then you have a fully functioning pancreas and you would benefit by focusing on your blood sugars before you eat if you have more weight to lose.
In the Nutritional Optimisation Masterclass and Data-Driven Fasting we set even tighter limits than this. We recommend that people look to reduce the processed carbs in their diet if their blood sugars rise by more than 1.6 mmol/L or 30 mg/dL.
The chart below shows the hourly glucose chart from our Data-Driven Fasting app. In the first week of our Data-Driven Fasting Challenges, we guide people to dial back their carbohydrate intake to avoid overfilling their glucose fuel tank. But once you’ve ticked that box, you only need to focus on your premeal blood sugars to make progress.
The average blood sugar rise of people following Data-Driven Fasting is only about 10 mg/dL or 0.5 mg/dL (not much at all)! It seems people who are fans of fasting (and typically following a low carb or keto diet) already have extremely stable blood sugars!
Stable glucose does not equal fat loss!
As shown in the charts below, people who have a higher waist:height ratio and BMI only have a slightly larger increase in blood sugar after they eat.
The correlation is extremely low (i.e. there is no relationship).
The correlation between the amount your glucose rises after you eat and your waking glucose (another key marker of metabolic health) is also non-existent.
It seems, while normal, healthy, stable blood sugars are a good thing, flat line is not better!
Although stable and lower blood glucose levels are a positive marker of metabolic health, merely treating the symptom (i.e. elevated blood sugar) rather than addressing the cause (i.e. insulin resistance, energy toxicity and excess body fat) doesn’t help.
Unfortunately, many people who believe that fat is a free food because it does not raise insulin levels end up overeating refined fat to maintain stable blood sugar levels. Before long, this leads to fat gain and worsening insulin resistance.
Sadly, there are plenty of keto gurus and their die-hard believers who continue to gain weight because they are trying to optimise the wrong numbers!
When we look at glucose variability (i.e. standard deviation/average glucose), we see that there is also a negligible correlation between stable blood sugars and a better waist:height ratio, BMI or waking blood sugars.
Many people have combined fasting with a high fat keto diet in an attempt to achieve stable blood sugars in the hope of weight loss. But sadly, in spite of their Herculean feats of self-deprivation, they just continue to gain weight due to a low satiety nutrient-poor diet that leaves them craving and eating more when the fast is over. As shown in our survey in our Data-Driven Fasting Group, losing and regaining the same weight over and over is very common with popular fasting protocols.
Actively avoiding insulin and any normal rise in blood sugar levels using a high-fat diet tends to lead to poorer satiety, greater energy intake and obesity. In time, these people often end up with higher insulin levels across the day because they are carrying more body fat which requires more insulin to hold in storage.
The good news is, we see a better correlation between pre-meal glucose and waist to height and BMI. Rather than worrying so much about your blood sugars after you eat, it seems that people who have a lower blood glucose before they eat tend to have much better metabolic health.
There is some variability across individuals due to different Personal Fat Thresholds. However, when we look at this person by person (e.g. Jane’s data below), we see that a lower premeal glucose trigger before you eat aligns nicely with weight, waist to height and body fat levels.
You can check out my interview with Jane (pictured below) here.
Your waking glucose is one of the most reliable indicators of metabolic health and your risk of dying from any cause.
As shown in the chart below, pre-meal blood glucose trigger strongly correlates with your waking glucose. Rather than worrying about the rise in glucose after you eat, managing your glucose before you eat is much more useful if you actually want to lose fat and gain health!
To optimise body composition, you need to measure and manage the things that matter. Your blood sugar before meals is a much more useful metric that you can manage by optimising your meal timing and intermittent fasting routine.
Doesn’t WHAT I eat matter too?
Yes. WHAT you eat is arguably more important than WHEN you eat.
Data-Driven Fasting simply empowers you to optimise your food timing to ensure a negative energy balance.
- While high-fat foods and meals will keep your blood sugars stable, they also provide a lot of energy and lower satiety. Although your blood sugars and insulin levels may be stable, your body won’t need to draw down on your body fat for a long time until it burns up all the energy from that fat bomb or buttered coffee.
- Meals with more fast-digesting non-fibre carbohydrates will raise your blood sugars quickly, but they may return to below baseline more quickly.
- Foods that contain both fat and carbs together (and low protein) will fill your fat and glucose fuel tanks at the same time and allow you to eat more and keep your blood sugars elevated for longer.
- Foods with a higher percentage of protein and a greater nutrient density are harder to overeat and won’t raise your blood sugars significantly (in fact, they may reduce them).
The bottom line
- Lower and stable blood sugar and insulin levels are a sign of good metabolic health, but managing the symptoms with a high-fat diet does not lead to metabolic health.
- The fundamental problem is not insulin toxicity. It’s energy toxicity.
- When you eat, rather than focusing on avoiding short term blood sugar and insulin spikes, you should focus on higher satiety nutrient-dense food that will reduce your cravings and allow you to lose body fat.
We designed Data-Driven Fasting to solve the energy balance problem and avoids the many pitfalls and shortcomings of calorie tracking. Using your blood sugars as a fuel gauge to return to just below your personal trigger ensures a long-term negative energy balance. Over time, insulin, blood sugars, waist, body fat and improved metabolic health will follow.
If you want to find Your Personal Trigger you can download our free baselining sheet here or download our free 130-page Data-Driven Fasting Manual here to learn all about how you can use Data-Driven Fasting to fine-tune your intermittent fasting routine to optimise your pre-meal blood sugars.
To learn more, you can:
- Download the (Free) Data-Driven Fasting Manual,
- Join the Data-Driven Fasting Facebook Group, or
- Join the next Data-Driven Fasting 30 Day Challenge.
Data-Driven Fasting Index
- Data-Driven Fasting
- Download the manual (PDF)
- Facebook Group
- QuickStart Guide
- Success stories & results
- FAQ #1 – What makes DDF different?
- FAQ #2 – Getting ready
- FAQ #3 – Tracking your progress
- FAQ #4 – WHEN to eat
- FAQ #5 – WHAT to eat
- FAQ #6 – Winning the mind game
- FAQ #7 – Understanding your unique metabolism
- FAQ #8 – Troubleshooting
- FAQ #9 – Things that affect your blood sugars (other than food)
- FAQ #10 – Moving on…
- Join the next 30-Day Challenge