This is a practical Blood Glucose Testing Guide covering why and how to use blood glucose testing to discover your highly personal blood glucose response to different foods. Understanding the response that different foods provoke for you enables you to make informed choices that can lead to improved health and well-being in the short and long term.
Within this guide I cover the basics of what blood glucose testing involves, why do it, and what you might discover. Also included are directions to resources and the tools that you will need. To help you plan, record and analyse your own results I share a Blood Glucose Testing DIY Template via Google Sheets.
Accompanying this guide is a Results and Reflections post presenting & discussing my own blood glucose testing outcomes.
I emphasize I am a citizen scientist and not a medical professional. I am also neither diabetic or pre-diabetic. My ambition is that this guide is of value to anyone wanting or needing to learn about their blood glucose and make positive changes within their diet but please do take medical professional advice if you have a condition to manage.
Why care about Blood Glucose responses to foods?
The short answer in 5 key points and one big picture.
- Blood glucose is a good proxy measure for insulin and gives information about your insulin sensitivity
- Insulin sensitivity has an enormous influence on multiple health outcomes
- Insulin sensitivity is strongly influenced over time by your dietary choices
- Insulin response to different foods varies considerably between people
- Testing your blood glucose responses to foods can give you insights that enable better dietary choices
What benefits can be gained from blood glucose testing?
Outcomes from testing include.
- General learning about your own level of insulin sensitivity
- Discovering your personal blood glucose response to different foods
- Discovering food sources that result in large or abnormal blood glucose responses
- Discovering foods that result in low blood glucose responses
- Learning how lifestyle choices and daily behaviors may impact on your average blood glucose
- Gaining actionable insights that can inform dietary choices that are healthier for you
These in turn may enable you to:
- Improve your own insulin sensitivity
- Reduce your HbA1C average blood sugar level
- Reduce your risk of diabetes and other chronic illnesses associated with insulin resistance
Best of all, testing your blood glucose testing is relatively simple and not hugely expensive.
Personalized Nutrition, Carb Testing, and Blood Glucose
The rest of this post is structured in a series of steps to help you carry out your own n=1 self-experiment to learn about your personal blood glucose responses to foods.
The guide content is based on my direct experience of conducting an n=1 experiment with a protocol that drew upon the 7 Day Carb Test plan offered by Robb Wolf and the study protocol used by the ongoing Personalized Nutrition Project led by the Weizmann Institute of Science.
I offer a Blood Glucose Testing DIY Template via Google Sheets to help you plan and capture results from testing. This sheet is publicly accessible. To edit it for your own use simply make a copy first.
I am intending to perform further rounds of testing myself and greatly welcome comments, questions, tips and recommendations within comments. This post is one of a pair. Within a separate Results and Reflections post I cover everything I observed and learned from my first round of testing.
Step 1: Define your Goals
Write down what you want to actually gain from testing. What are your motivations? What benefits do you want to get from testing? Some examples follow.
- Do you want to focus on actionable insights?
- Are you willing to commit to changes following testing?
- Which foods do you want to learn about your personal responses to and why?
- Do you have a specific goal such as reducing your HbA1C?
- Do you want to avoid blood glucose peaks and troughs that provoke brain fog, hunger and unhealthy snacking?
- Are you seeking to make better choices for weight control or reduction?
Step 2: Select & Practice with your Testing Tools
You need a way to take multiple measures of your blood glucose. There are two I have direct experience with and can recommend.
Flash Glucose Monitor by Freestyle Libre
A Flash Glucose Monitor involves attaching a sensor to the back of your arm. Whilst active the sensor will enable you to take frequent readings using a simple device or your smartphone. Highly convenient and for dedicated testing also cost effective given the number of readings is effectively unlimited. Note that the Libre Sensors actually take results from interstitial fluid rather than blood. Correlation with blood glucose is supposed to be high.
As of December 2017 the Freestyle Libre only offers a Smartphone App for Android which means a dedicated reader is needed for iOS users. An iOS App is expected by February 2018.
Finger-Prick Glucose Monitor & Testing Strips by On-Call Dual GK Meter
More reliable than Flash Glucose Monitors given that results are taken direct from blood rather than interstitial fluid. Test strips are cheap and finger-prick testing is simple, quick and involves minimal discomfort once you have a little practice. Not ideal however for taking lots of measurements in a short period of time.
For greater reliability and accuracy it is ideal to use both devices rather than one alone as this enables you to use one device to validate the results from the other if they differ considerably.
There are other options for tools indicated within the Blood Glucose Testing DIY Template.
Practice before Testing!
If you are entirely new to testing with a finger prick device get some practice before beginning your testing regimen. Some resources to help you follow are this written and illustrated guide to finger prick testing and the youtube video demonstration below.
Step 3: Establish your fasted baseline
I recommend two things to establish your baseline prior to testing and any changes you make following testing to your diet.
Fasted Blood Glucose Tests
Take several blood glucose tests after waking and before your first meal. This should be done at the same time each day for consistency since blood glucose can even in the absence of food intake. For example, if you normally wake at 7am and eat breakfast at 8am, take your fasted baseline measure between 7am and 8am. This helps establish a baseline from which you can begin your food testing.
You may find that your fasted baseline is stable or varying. There is something called dawn phenomenon which can result in high morning fasted blood glucose. This is common for diabetics but affects others too including those with great insulin sensitivity.
If you experience varying levels that is okay. You can still perform food testing and measure the delta between whatever level you start from that day and the peak following the food you consume. However knowing the starting point relative to your own baseline is very helpful context for interpretation of results and you may choose to defer a test if your starting blood glucose is abnormally high in order to get a cleaner set of results for interpretation.
In contrast to a single or several fasted blood glucose tests a HbA1c test (glycated haemoglobin, haemoglobin A1c) provides you with information about the average levels of glucose in your blood over a period of about 3 months. Read more about the purpose and interpretation of HbA1c tests at diabetes.co.uk
If you are diabetic or at risk of diabetes you may very well be able to arrange a HbA1C test through your healthcare provider. They are also available as direct to consumer tests. The Blood Glucose Testing DIY Template includes a link to a UK provider of direct to consumer HbA1C tests.
Step 4: Select your Test Foods
The Robb Wolf 7 Day Carb test protocol focuses on foods that are mostly just carbohydrate rather than meals or foods with significant protein and fat. That protocol is particularly suited to specific exploration of carbohydrates that you might be personally intolerant despite being considered “healthy”. So for example, you might choose sweet potatoes and wholegrain bread.
My advice is –
- Include within your test a pure glucose / dextrose sample to give yourself an excellent benchmark for comparison
- Choose foods that you actually eat or are interested in eating if you want actionable insights
- Consider Including some contrasting foods, for example white bread and wholegrain bread, white rice and wild rice, in order to observe how differently you respond to them
- Choose as many foods as there are days that you intend to conduct testing for
In addition or as an alternative to the 7 Day Carb test protocol you can also choose to test conventional meals and snacks. If you do this consider a few of the following approaches.
- Test the the same meal twice but vary the order in which you eat the food, for example for a meal of soup and bread, try eating the soup first then the bread, and vice versa. There is study evidence showing that the order in which foods are eaten is influential on the total blood glucose impact
- Experiment with adding Apple Cider Vinegar to a meal. There is some evidence that Apple Cider Vinegar can reduce blood glucose levels in both rats and humans
- Take a simple meal and adjust one ingredient within it that you expect may impact on the response. Try adding a source of fibre or fat in order to observe what impact this has. The Personalised Nutrition Project compared bread alone with bread plus butter for example.
- Take the same meal and monitor the response to it when eaten in the AM and in the PM. There is evidence that some people are more sensitive to carbohydrates eaten in the evening
- Get creative and have fun, include some foods that you think of as ‘healthy’ and some you think of as ‘unhealthy’. Maybe throw in a Black Forest Gateau Hot Chocolate with Cherry Sauce & Whipped Cream. Seriously, this is a real thing, with 60 grams of real sugar! Don’t get hooked!
Step 5: Plan and Prepare your Food
To directly compare carbohydrates against each other as per the Robb Wolf 7 Day Carb Test protocol you need to calculate how many grams of each chosen food will deliver 50 grams of Net Carbs. This is done to enable like for like comparison. Prior to the Personalised Nutrition Project the amount of carbohydrate in a meal was the best and strongest predictor for blood glucose response.
Whilst determining Net Carbs be aware of the difference between US and Euro food labels when determining net carbohydrates.
Euro Food Labels: The Carbohydrate number is the Net Carb number already, ready to use. Fibre is listed separately and is excluded from the Carbohydrate number. The Sugars number is included within the Carbohydrate number.
US Food Labels: The “Total Carbohydrate” or “Carbohydrate” number includes the Fiber number. Calculate Net Carbs by deducting the Fiber from the Total Carbohydrate.
The DIY Blood Glucose Test Template includes a simple calculator to determine how many grams of food you need to have 50 grams of carbohydrate. For example, if a food has 40 grams of net carbs per 100 grams, you need 125 grams total. Euro food labels make this easier by always providing per 100 gram data. For US labels, multiply the Net Carb value by 100 / Serving Size Grams to get the Net Carbs per 100 grams.
If you will be testing whole meals it is not necessary to target 50 grams net carbs since you are simply interested in the response to the full meal. However to help you analyse I recommend plotting the meal into CRON-O-Meter. This will let you see how many grams of protein, carbs, sugar, fiber and fat there were in the meal and enable comparisons between meals.
If using a Flash Glucose Sensor with a limited life span make sure you have several days of foods lined up ready to test so you do not miss out on any test day opportunities. If using Finger-Prick test strips you can easily skip days as suits you.
Step 6: Start Testing
On your testing days take a fasted baseline test and record the score. Then eat the test food and note how long it took you to eat. 50 net carbs worth of dates can be eaten in a couple of minutes. 50 net carbs worth of hummus or bread will likely take significantly longer and knowing this may be useful.
Try to limit the variables that may influence results. You can do this by:
- Beginning the tests at the same time each day
- Not drinking anything other than water before and during the test
- Not exercising before or during the tests
If you are using a Flash Glucose Monitor I suggest taking measures every 15 minutes for 4 per hour. This provides sufficient detail to show the speed of response, peak and how long blood glucose takes to return to baseline.
You can do the same with finger-prick tests. 10 tests, one per finger, can cover the baseline and up to the 2 hour 15 mark and this will likely be enough to observe blood glucose return to fasted baseline levels for most foods and meals. You could however take fewer measurements, one every half hour, and still benefit from most of the information value.
Robb Wolf suggests taking just two measurements. One pre-feeding and at the 2 hour post-eating mark. Arguably this will give you all you need to know to understand the impact of a given food on your insulin. Comparing the 2 hour mark measure from food to food tells you something about –
- Impact relative to other foods
- Total insulin / blood glucose impact
However what it doesn’t tell you is:
- How high the blood glucose peak was prior to the 2 hour mark
- How long it takes your blood glucose to return to fasted levels following that peak if not complete by 2 hours
So if you have the tools and the willingness to take more frequent measures my recommendation is to do so. The extra data you gather may be interesting and valuable when you begin analysis. At the very least it enables you to look at charts with the blood glucose plotted in a curve. For examples, jump over to my Results & Reflections post.
Step 7: Analyse your Results & revisit your Goals
The DIY Blood Glucose Test Template has a ready made table and charts to capture and graph:
- Blood glucose measures
- The delta between your fasted baseline and peak blood glucose level
- The blood glucose curve as it rises, stabilizes and then returns to baseline over time
The charts I have set up also have dotted lines to indicate
- The top end of the ‘normal’ range for fasted blood glucose
- The top end of the ‘normal’ range for 2 blood glucose two hours after eating
The ‘normal’ values are those given by diabetes.co.uk and are:
- Fasted glucose of 4.0 mmol/L to 5.9 mmol/L (or (72 mg/L to 106 mg/L)
- Two hour post-meal glucose of 7.8 mmol/L (or 140 mg/L)
Simple inspection of the deltas and charts can show you:
- The total blood glucose response to each food tested
- The blood glucose response relative to other foods
- The peak blood glucose reached and the delta between this and the fasted baseline
- Time taken to return to fasted baseline
- Whether blood glucose dips below fasted baseline on the decline i.e. a blood glucose ‘trough’
For inspiration and points of reference for making sense of your own results, I recommend reading my own Results and Reflections post within which I share my results and thoughts. There are similar results shared and discussed in posts from Quantified Body and Lateral Eating.
Blood Glucose Testing Guide DIY Template
Note that to be able to use the Blood Glucose Testing DIY Template for yourself you simply need to make a copy by opening the template then going to File > Make a Copy. Once you make a copy you can freely edit the copy.
If you are thinking of testing yourself, or you actually test, go ahead and tell me about your results. Did you find anything unusual? Did you make any changes based on your findings? I am planning further testing myself and would love to share insights.
Keen to share? If you have a set of results and you would like to share them widely contact me. We could prepare a guest post together for publication.