It’s generally accepted that it’s a healthy idea to avoid spiking your blood sugar. Spiking your blood sugar regularly can cause insulin resistance, obesity, cancer, heart disease, stroke, type 2 diabetes, and so on. Some years ago I came across a study from Drs. Segal and Erinav of the Weizmann Institute which proved to my satisfaction that different people may have different glycaemic responses to the same foods. In other words, a croissant may spike my blood sugar but not yours. And I may be able to get away with eating chocolate that would send your blood glucose through the roof.

Why does this matter?

Well, there is no field of human health more riven with disagreement (in the scientific literature and in popular culture) than what we should eat. It’s massively affected by culture, family tradition, and contradictory studies demonising this way of eating or praising that. You can see my approach so far here. Leaving aside the ethics of what you eat (such as animal welfare, climate change, and so on) and looking purely at health outcomes, it is impossible to determine one diet that works for everyone. The Weizmann study went a long way towards explaining why this is the case: we all respond differently to the foods we eat.

Consider some of the variables in play when a specific food (such as that delicious croissant) hits your digestive system:

1. Human genetic variation, which affects digestion, enzyme production, etc. etc.

2. Gut biome variation, which also affects everything from mental health to nutrient absorption.

3. Environmental factors (such as the historic availability of certain foods to your immediate ancestors, your exposure to various chemicals, the list is endless).

4. Exercise, which affects blood sugar levels- intense exercise causes the breakdown of glycogen, for instance, raising blood sugar levels, if only briefly. It also affects blood distribution (away from the gut and into the muscles, for instance).

5. Time of day: bodies operate on a circadian rhythm, and will respond differently to different stimuli and different times. 

6. What else is ingested with the croissant: marmalade? Ham? A glass of orange juice? Lots of artificial additives?

7. We’re talking about human beings here, so psychological factors such as the placebo and nocebo effects are probably also significant.

8. People change over time, so what happened last month may not happen today.

This makes it effectively impossible to predict safely what effect a particular food will have on a particular person. Sure, broccoli is less likely to spike blood sugar than ice-cream, but that ice-cream may actually be fine for you, but not for your friend sitting next to you on the couch holding a spoon. And a virtuously lo-carb steak may act on your pancreas like a boxful of doughnuts does on mine.

It would be easy and natural to throw your hands up in despair and cry “it’s too damn complicated, I’ll eat what I like!” But if you accept the idea that once you are getting sufficient nutrition the most important issue of diet is to avoid blood sugar spikes, then there is an Alexandrian Sword at hand to sever this Gordian Knot.

Enter the blood glucose monitor. Familiar to every diabetic, and costing considerably less than a night out in a decent restaurant, it promises to separate truth from falsehood. I’ve bought one, and am about to start measuring my blood sugar on waking (to establish my baseline), before every meal, and at intervals after every meal. With that data and a food diary, after perhaps a week or two I should have a good idea of what foods I’m commonly eating that I should avoid, and what foods I’m commonly avoiding that I could be eating (I am praying that Nutella on toast will leave my blood sugar remarkably unchanged…). If a particular meal spikes my blood sugar, I’ll try eliminating the most likely culprit within the meal (such as switching out rice for more vegetables), and see what that does. 

There is no sense in testing individual foods individually; it would take forever, and as the food combinations are also a factor, it would produce false positives and false negatives. Nutella out of the jar with a spoon is not the same as Nutella on a banana (oh my goddess that is delicious). 

In this way I should be able to get a handle on what works for me. As I’ve been saying for years, the key to success in any field, including diet, is find out what works for you then do that. So you may be wondering why I haven’t gone the glucose monitoring route before now. I think its a combination of being basically happy with my diet, weight, etc., so I’ve got no feeling of urgency about this, and I fucking hate needles. Literally my entire job is finding out ways of not getting stabbed. I’m not fussed about blood; as a woodworker I bleed regularly- I once counted 13 separate scabs on my left hand alone. I just don’t like needles. Fortunately, a modern blood testing kit uses a special lancing device, so you don’t actually see the needle. And, not being diabetic, I won’t have to inject myself at any point.

After my blood glucose monitor arrived last week I thought to re-check the study that set me off on this… and wouldn’t you know, Drs Segal and Erinav have a book out: The Personalized Diet (affiliate link). I read it straight away, and it goes into the background of their research, the argument for using blood sugar monitoring as a way to measure whether a food is good for you or not, the gut biome and why it’s important, and even a detailed description of when and how to go about measuring your blood sugar, how to record your findings, and so on. If you don’t want to take my word for this blood sugar thing (and why the hell should you? I’m a swordsman, not a medical doctor or nutritionist) then buy the book or get it from your local library. How I missed this when it came out in 2017 I’ve no idea- except perhaps I was already sold on the idea from the study, and so stopped looking.

I should also note that blood sugar spiking is not the only measure of a food’s effect. Allergies and sensitivities are also important. Nutritional content is obviously key: just because Nutella on toast doesn’t spike my blood sugar doesn’t mean it’s actually good for me, or constitutes a complete and healthy diet. If I find there are nutritionally important foods that I shouldn’t eat, I’ll have to find substitutes for them. Maybe cabbage replacing cauliflower. And, let’s face facts. Unless a food is directly and immediately fatal, if I love it I won’t eliminate it completely, metabolic consequences be damned. My daughter baked this Pride cake recently: see the rainbow?

No way in hell I’m not having a slice, regardless of what it does to my blood sugar. But it would be helpful to know for sure what foods are bad for me in this respect.

If I was a proper modern person I’d no doubt do a daily vlog sharing my blood sugar data, details of my diet, etc., etc. But I’m not. The very notion of telling the world what I had for breakfast is just weird. What I will do though is report back with my experience of doing this, and my findings, whatever they may be. Wish me luck with the Nutella thing…