The Best Way to Guide Your Weight Loss Using Your Glucose

In a world where just about everything can be quantified, data is easy to come by.  

There is no shortage of fancy-sounding biomarkers that you can track.  

But sadly, wise interpretation is rare, and confusion abounds!  

No one really wants to spend their limited time, attention and mental bandwidth (not to mention hard-earned cash!) measuring the wrong things.  

In this article, you will learn why your blood glucose BEFORE you eat is the most useful thing you can use to manage your weight, body fat and optimise your metabolic health.  

Most people don’t want to be full-time biohackers:  They just want to measure what matters, get results, and get on with living their best life.

We have seen hundreds of people achieve great success as they use their pre-meal blood sugars to validate their hunger and to understand if they really need to refuel.

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What are we trying to achieve?

Many people struggle to solve the energy balance equation when food is cheap and plentiful.  

While energy is always conserved (calories count if you can count ALL the calories accurately), simply telling people to ‘eat less and move more’ rarely works over the long term for free-living humans.  

In a world of engineered hyperpalatable foods, it’s no wonder we have lost touch with our true hunger and healthy appetite signals.  

In spite of applying all the willpower we can muster, many of us are losing the battle with obesity.  

Chronic energy toxicity leads to diabetes, heart disease, cancer and a whole host of modern diseases that come under the banner of ‘metabolic syndrome’ or insulin resistance.  

We are becoming increasingly overfed but undernourished at the same time.  We believe that satiety and nutrient density are critical factors in winning the battle with your appetite.  

Still, many people are searching for ONE magic number to guide their eating decisions.  

  • What can you track to balance the calories in vs calories out equation?   
  • What is useful?  
  • What is a waste of time?  

Before I tell you why your blood glucose before you eat is the most useful parameter that you can track, let’s look at the pros and cons of some of the other options.  

Weight and body mass index 


  • Weight is easy to measure.  Most people have a bathroom scale.  
  • Weight and body mass index (BMI) are loosely correlated with metabolic health.  As shown in the chart below, a BMI around 24 seems to be ideal in terms of longevity.
  • A downward trend in weight may indicate you are making positive changes in your diet and lifestyle.  


  • Your weight can vary from day-to-day depending on many factors including what you eat, your activity levels, sleep, mineral intake and that time of the month for women.
  • BMI isn’t particularly meaningful for someone carrying more muscle mass average.  Having a low BMI because you are ‘skinny fat’ is not ideal either.
  • Many people struggle mentally with fluctuations when they use their weight as their primary measure of success.  They fail to look at the long term trend and become discouraged.  
  • Your weight on the scale doesn’t differentiate between metabolically active lean mass and your fat mass (which most of us are trying to reduce to healthier levels).   
  • As you improve your diet and become more active, your lean mass may increase while you are losing fat, but the scale may not reward you with a ‘better’ number.  

Body fat percentage


  • Rather than losing weight, most people need to lose fat and gain more strength (i.e. lean mass), so it’s really more useful to track your body fat percentage, lean mass and fat mass.
  • You can manage excessive loss of lean mass in caloric deficit by making sure you consume adequate dietary protein.


Waist-to-height ratio


  • Your waist-to-height ratio is a great indicator of your metabolic health and is more powerful than weight alone.  As shown in the chart below, a waist-to-height ratio of around 0.5 seems to be ideal.   


  • Your waist measurement changes slowly, so it doesn’t tell you much about how your diet is working for you on a day to day basis and what you need to change to move toward your goals.




  • Insulin is a laboratory blood test, and In some countries, it can be difficult to get.  
  • Unless you are injecting it, insulin is a lagging marker.  Your pancreas will never produce more insulin than is required to hold your energy in storage while you have food coming in via your mouth.  Many people incorrectly believe that the insulin from their own pancras is making them fat, when the reverse is actually true: their pancreas is working overtime to produce insulin BECAUSE they are fat.
  • Your insulin response to meals is small  compared to the insulin required to hold your energy in storage.  Many people who are concerned about ‘insulin toxicity‘ tend to try to minimise their insulin response to meals (i.e. bolus insulin) by switching carbs and protein for fat.  However, they ignore the fact that the majority of the insulin produced by their pancreas is simply a response to the amount of body fat they are carrying.  
  • The best way to manage insulin levels is to reduce how much and how often you eat.

Blood ketones 


  • Blood ketones are often present in the early stages of fat loss when someone enters an energy deficit and they turn to stored body fat for fuel (i.e. endogenous ketosis).  
  • Many beneficial things occur when we eat less and move towards a more optimal body composition.  Our body goes into repair mode as we clean out all the excess junk in our body (i.e. autophagy).


  • Blood ketones are simply the storage and transport form of ketones.  Rather than providing an indication that you are burning fat from your body, your blood ketones tell you how much energy you have backing up in your system that you’re not yet burning.  
  • Blood ketone values are hard to interpret meaningfully.  Your elevated ketones may be due to the fact you are eating less protein and carbohydrate and more dietary fat than your body can use (i.e. exogenous ketosis).  This scenario does not lead to fat loss from the body or improved metabolic health.  
  • Blood ketones tend to decrease over time as people lose weight, reverse their diabetes and improve their metabolic health.  So to maintain elevated ketones over the long term you need to add more and more dietary fat, which is counterproductive if your goal is fat loss and improved metabolic health.
  • The term ‘ketogenic diet’ means a lot of different things to different people, but generally, a very high-fat, low-protein diet tends to provide fewer nutrients and satiety per calorie.
  • Blood ketone strips are expensive and can be difficult to get.
  • Blood ketones provide little useful information to guide our food choices.  It’s impossible to know if your high ketone levels are due to endogenous ketosis (i.e. you are burning body fat) or exogenous ketosis (i.e. you are burning fat from your diet).

Breath ketones 

After realising the many limitations of blood ketones, many entrepreneurial companies and keto enthusiasts are turning to breath ketones (namely acetone).  My podcast and Instagram feed at the moment seems to be full of people promoting their new breath acetone device or systems to use in conjunction with continuous glucose monitoring (CGM) data (hence, the inspiration for this article).


  • Breath acetone is produced when the body oxidises ketones for fuel.  Hence, breath acetone provides a more useful indication that you are actually burning fat (rather than simply causing excess energy to back up in your body).  
  • When combined with blood glucose data, breath acetone can provide a useful indication that you are achieving endogenous ketosis.  If your blood glucose is low and your breath acetone is high, you are likely burning fat from your body, not from your diet.  See Is the acetone:glucose ratio the Holy Grail of tracking optimal ketosis levels? for more detail.


  • Similar to blood ketones, you can also ‘cheat the system’ by simply eating more fat.  
  • The measurement you get from your breath acetone meter can depend on your technique (i.e. you have to get the breath from deep in your lungs).  
  • Although there is no ongoing cost, breath ketone devices are expensive to purchase.  
  • Breath acetone tends to rise after blood ketone values.  This makes sense when you understand that breath acetone is an indication that the ketones in your blood are being burned.  However, this lack of correlation between breath and blood ketones can be confusing for some people.  

After meal (i.e. post-prandial) blood sugar 


  • Wild swings in blood sugar can cause increased hunger and appetite.  Reducing your intake of refined carbohydrates to the point you achieve healthy non-diabetic swings in your blood sugar (e.g. a rise of less than 1.6 mmol/L or 30 mg/dL) is useful to ensure you are not eating because your blood sugar is dropping too fast.  


  • We tend to think that more is better, and hence if healthy stable blood sugar is good, therefore a flatline must be better.  However, this is not the case.  Simply having more stable blood sugar does not necessarily mean that you will be leaner or have better metabolic health.  

Continuous glucose monitoring (CGM)

CGMs are expensive, but they are becoming more accessible and popular for people who do not have diabetes.  Many entrepreneurial companies are jumping on the bandwagon to try to tell you how to interpret your CGM data to guide your diet.  However, more data is not necessarily better and can be dangerous when you are following bad advice.  

Understanding how your blood sugar responds to the food that you eat can provide some fascinating insights.  However, few people understand how to interpret this data to make meaningful changes to their diet.  As they say, a little bit of knowledge or data can be dangerous.


  • CGMs provide amazing insights for people with diabetes.   If you are injecting insulin, it makes a lot of sense to work to reduce dietary inputs that require large doses of insulin.  As per Dr Bernstein’s Law of Small Numbers, stable blood sugar enables more accurate insulin dosing and more stable blood sugar aids appetite control.  


  • CGM day can be overwhelming for many people.  I love data and spend a LOT of time watching my wife’s live CGM feed and trying to fine-tune her closed-loop insulin pump system.  For me, as a data-loving engineer, this is often overwhelming.  I see many people in our Data-Driven Fasting using CGMs and losing their minds and getting confused as they try to understand the minute-to-minute fluctuations in their glucose.   You can definitely use a CGM with Data-Driven Fasting, but people tend to have better long-term success (and not burnout in the short term) when they use a simple glucometer a couple of times a day.
  • Leaner people with good metabolic health have more stable blood sugars.  But, simply eating to achieve stable blood sugars is merely symptom management and does not necessarily lead to improved metabolic health.  
  • The combination of being confident and wrong at the same time is dangerous. There are a number of ways you can screw this up and make things worse. 
    1. One way to achieve stable blood sugars is to eliminate all carbohydrates and even protein and consume a high-fat ‘ketogenic diet’.  However, as noted above this can just lead to excessive intake of low-satiety nutrient-poor foods.  While some advocate for eating ‘fat to satiety’, fat provides the lowest satiety relative to the other macronutrients.  See Optimising food for satiety: How to tame your hunger monster for more details
    2. One method I’ve heard CGM advocates recommending to achieve more stable blood sugars is to add fat to your carbohydrates (e.g. add butter to your potato).  While this may taste great and look better on your CGM, the combination of fat and carbs together is even worse than fat alone in terms of satiety, and leads to excess energy consumption, which will lead to worsening insulin resistance.  The combination of fat and carbs with lower protein is the formula for low-satiety junk food (e.g. doughnuts, croissants, cheesecake, cookies).  
    3. People get shocked by the swings they see from carbohydrates and suddenly assume that they should avoid all carbohydrates.  But they miss the fact that, although their blood sugars rise quickly, they often fall quickly, often to lower levels than before they ate.  It is hard to overeat whole-food carbs without added fat.  While there is no need to prioritise refined starches and sugar, there is no need to fear whole foods like vegetables, which provide more satiety per calorie than the high-fat options, even if they cause short-term spikes on your CGM.
  • Many are confidently going down the wrong path due to the ‘insights’ from their CGM.  While you may flatten the spike, the fat+carb combo generates the biggest area under the curve insulin and glucose response as your body processes the excess energy for many hours.  
  • Rather than worrying so much about short-term stability, it’s much more useful to focus on bringing your blood sugar and insulin levels down across the whole day.  This is achieved by finding a sustainable way to eat less.

Blood cholesterol 



  • It requires a laboratory blood draw, so it is difficult to do regularly (unless your name is Dave Feldman).
  • People who follow a low-carb diet tend to have an ‘abnormal’ cholesterol profile compared to the majority of the population who are consuming a high-carb diet.  
  • There is endless debate about what a ‘good’ cholesterol profile is and how to modify your diet to tweak it.  In the end, it comes down to managing body composition and not having excessive levels of glucose and fat floating around in your bloodstream at the same time.  See Cholesterol: When to worry and what to do about it for more details. 

Respiratory quotient


  • The Respiratory Quotient (RQ) is a fascinating test that you can do to tell if you are burning more fat or glucose.  Interestingly, most people who are obese or insulin-resistant are burning mainly glucose at rest in spite of carrying a lot of body fat.  
  • Due to oxidative priority, your body works to burn off excess glucose in your system first, before it starts to use fat.  This makes sense when we understand that people with type 2 diabetes have exceeded their Personal Fat Threshold and energy is backing up in their system.  Energy not able to be stored is overflowing into their bloodstream.
  • If your RQ indicates that you are burning mainly glucose, it makes sense to reduce the carbohydrates in your diet to allow your body to access stored fat.  


  • The laboratory equipment required to do this indirect calorimetry testing is expensive, and hence the test is not don’t regularly done outside a research setting.  
  • Some handheld devices are starting to use a scaled-down version of this technology and marketing to the consumer.  However, these devices are still very expensive.  
  • If your waking blood sugar is elevated, it’s highly likely that your body is struggling to burn off excess glucose backed up in your system and you would benefit from reducing the processed carbohydrates in your diet (and maybe the fat too) to allow your body fat to be used.  There is little additional value in knowing your RQ.  



  • Energy balance is a thing.
  • There are many options available for convenient calorie tracking (e.g. Cronometer).


  • Both sides of the calorie in vs calorie out equation are incredibly complex.  
  • Most people fail in the long run when they simply try to reduce calories.
  • Aiming for a fixed calorie target can leave you hungry some days and overeating on others.  Outsourcing your satiety signals to a smartphone app rarely ends well.  
  • Tracking calories does little to train your true hunger signals.  In fact, it puts you in constant conflict with your ‘lizard brain’.  This is a fight we typically lose.

Pre-meal blood sugar 

Finally, we come to your pre-meal blood sugar.  Most people don’t want to be full-time biohackers, but rather, use the minimum effective dose of measurement and quantification that will enable them to achieve their goals.  


  • Requires you to test your blood sugar a few times a day (similar to blood ketones).
  • There is a small amount of pain that can take a little while to get used to.   However, the act of testing works as a ‘pattern interrupt’ when you would otherwise mindlessly head to the fridge.  It forces you to consider whether you are really hungry or eating for another reason.  
  • Many things (other than the food you eat) can affect your blood sugar (e.g. sleep, stress, exercise, time of the month for women).  However, once we understand these other factors, we can filter out the noise and focus on the signal.  


  • Your blood glucose gives you an instantaneous indication of whether you need to refuel or can wait a little longer.
  • Over time, correlating your blood glucose with your sensations of hunger can help you to calibrate your true hunger, and understand and trust your appetite.  
  • Using your blood glucose works regardless of dietary preference (i.e. low fat or low carb).  
  • Monitoring your blood sugars before you eat empowers you to solve the energy balance equation without tracking your food.  
  • You will quickly learn which foods cause you to over fuel and tend to leave your blood sugars elevated for longer.  
  • Blood glucose meters and test strips are relatively cheap and accessible, particularly if they are covered by your health care system or insurance.  
  • Waiting to eat until your blood sugar has dropped below Your Personalised Trigger enables you to ensure that you are making progress and empowers you to gamify the weight loss process.
  • Unlike ketones and post-meal blood sugars, lower pre-meal blood sugars actually align with a better waking blood glucose, a lower BMI and better body composition.  
  • As you chase a lower pre-meal blood glucose value, fat loss and increased insulin sensitivity will follow as a result.
  • Tracking your pre-meal blood sugar enables you to identify the eating routine that works for your unique metabolism and schedule.  

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5 thoughts on “The Best Way to Guide Your Weight Loss Using Your Glucose”

  1. Phenomenal source of consistently great health information. One of my top go to sites. Thank you Marty for your outstanding work.

    • thanks! sadly everyone is focused on meal replacements and shakes rather than real food. whole foods that contain protein will be better in terms of satiety and nutrient density and will give better results.

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