7-Day Carb Test: How To Find Which Carbs Are Good And Bad For You

Intro

After experimenting with Keto / low carb diets for a while, I can tell that they were working for me quite well – at least from the aesthetic perspective. However, I always felt that I needed carbs in my life to support my CrossFit training– which due to relatively short and intense nature of workouts, favours glycogenic energy pathways that are primarily fuelled by carbohydrates.

That said, I have never been a fan of carbs, as from my early bodybuilding days carbs were synonymous to fat. For the sake of simplicity, I have to say that it is true (to an extent) – and you do have to choose between performance and aesthetics when it comes to nutrition. Therefore, no to lose visual benefits of CrossFit while maintaining good level of performance, I wanted to get smart about the carbs I eat. Not all carbs are made equal, so it is important to understand what works for you.

What you ideally want to find is foods that have the least impact on your blood sugar levels, i.e. the ones your body can process most efficiently – hence the testing concept is quite simple, eat carbs and measure their blood glucose impact. Robb Wolf’s 7 Day Carb Test method claims that it could help you with that.

This method appeared easy and cheap to do – small adjustment to your daily routine for 5-7 days (depending on a number of foods you want to test) and 5 minutes a day of the actual measurements so I could not wait and jump into testing it.

Science and claimed benefits

The general approach in the modern nutrition is to have foods with low GI index unless you specifically need high GI carbs, ie intra workout energy boost or post-workout recovery. However, it turns out that it’s not black and white and there are significant variations on how the same GI level foods are metabolised in different people and their impact on blood sugar.

This test claims that it would allow you to find what works for you as you see your body response vs someone else’s which might not be the same. More importantly, it is empirical rather than theoretical – you base your conclusions on the actual measurements you take instead of basing it on some ephemeral concept

How to use

The actual protocol is:

• Have the same amount of net carbs (i.e. less fibre) – in this case, 50g
• Nothing else should be consumed other than those carbs
• Have them under the same conditions – in my case first thing in the morning on an empty stomach
• Do not consume any other calories for the next two hours
• Measure your blood sugar levels and hope they are low

I added an additional step and measured my glucose levels before the test as well – given it is done first thing in the morning I can effectively measure my fasted glucose levels which are general indicators of insulin production and one of the diabetes indicators.

Then if the sugar levels are within 70-140 mg/dL – this food is good for you. If above such level – better to avoid that food. On the latter – the method recommends repeating with the lower dose of 25g net carbs but I have not done that.

I measured it using a basic finger prick tester you can buy in any pharmacy or Amazon. Other things to look out for are “brain fog” and energy levels – indirect indicators of insulin spikes.

Review

Regarding the carb selection – I am generally trying to eat gluten-free and paleo (ish), therefore removing many of the staple carbs out of the equation. Therefore I settled for the following:

• Red Beans (canned, in water)
• Sourdough bread
• Gluten free bread
• Orange Juice
• White Potatoe (frozen chips)
• Sweet Potatoe (frozen chips)
• Corn (nacho chips)
• Banana
• White Rice
• Brown Rice
• Oats (gluten free)

To sum my testing protocol up, I was waking up at c. 6 pm, measured my fasting glucose level, have a carb in question, then some water coffee in between, and measured my glucose again. I did some moderate training in the evening and tried to keep my sleep close to 8 hours to eliminate factors which might influence the results.
Also, I have made one control measurement to see how the levels evolve naturally, i.e. with no nutrition, therefore eliminating the Dawn effect which contributes to high sugar levels upon waking up – you can see it on the graph as “Fasting”.

The findings are the following:

• My waking fasted glucose levels are within the normal range and generally pretty close to each other at the beginning of each test
• Red beans, sourdough bread and orange juice created significant spikes in my glucose levels – well above the normal range. Moreover, after two hours they made my sugar glucose crash below levels of other foods – what is commonly referred to as “carb coma”. It is real and could clearly been seen on the graph, causing energy levels slump and sleepiness some time after eating such foods. It is important to note that these foods have their use i.e. when you need quick acting carbs – either just before an exercise to get energy boost or during / straight after exercise to quickly replenish depleted glycogen.
• Corn, white potatoe (chips / french fries) and gluten free bread – staples of “healthier” lifestyle (once you cut out sugars and gluten) still create spikes but those are within the normal glucose levels range. I would say those are ok from time to time but definitely should not form the base of your diet.
• Bananas, rice (both white and brown), oats (gluten free) sweet potatoe – I would like to be controversial but not today as foods which are generally deemed as “healthy” do show in my test the least impact on the blood sugar levels. Interestingly the white rice which frequently stigmatised as been bad for you – although having a bit of an impact on the sugar level, still is within the healthy range, and so are bananas. All these carbs are good backbone of carb intake in your diet and can be recommended based on my test.

Conclusion

I believe that the 7-Day Carbohydrate Test is a very effective way of finding out which foods your body prefers, and which foods create significant fluctuations in the blood sugar and therefore insulin levels. It’s a great way of quite cheaply and easily finding what you should eat more and less of – and take this test how to them once while if there are any outliers then retest those specific foods. I believe that’s a sensible middle ground and a good balance of efforts in and outcomes achieved.

Rating

Afterword

I definitely will do this test again in some time to a) retest these carbs one more time to ensure that the result holds over an extended period and not just a reflection of your short-term state – potentially changing the Impact score of this test and its Overall rating ; b) include more carbs into the mix in case An above holds – as if it doesn’t, and several testings of EACH carb is required, then the 7 day test would turn into 24 days test (3 tests for each of the carbs plus fasting baseline) – making it too cumbersome for most.

Secondly, as per above, I would prefer to do some more fasting baselines during the testing, i.e. not only one at the end of the test to get a more consistent view of the delta of fasting blood levels vs carb fed ones.

Separately I would try to get my hands on a continuous blood glucose monitor to ensure you capture the entire metabolic curve of a carb including its highest point – not just at the 1 and 2-hour points – by which it is most likely to have reduced. This test allows to capture that only via subjective indicators, and I would like to improve on that.

Measuring equipment

Glucose monitor – to measure the blood sugar levels (the one I am using).

Kitchen scales – to measure exact mass of food required to have 50g of net carbs (the one I am using).

References

• Robb Wolf. Wired to Eat: How to Rewire Your Appetite and Lose Weight for Good. Vermilion, 2017
• Diabetes.co.uk