Surely there are no downsides to trying to keep my glucose excursions low?
One of the problems with a glucocentric approach to nutrition is that the things you do to keep glucose low might be making your health worse in other ways.
Reducing circulating glucose, increasing circulating fats…..
One of the obvious ways that a person might choose to lower their blood glucose is to go very low carb. And yes, a diet with 8%kcal from carb, 70%kcal from fat and 15%kcal from protein FLATTENS glucose …..(chirpse the figure below):
..But this dietary composition also doubles circulating non-esterified fatty acid (NEFA) concentration.
It's also worth noting restricting carbohydrates to this degree doesn’t just raise NEFAs acutely, they remain increased over a prolonged period.
Now, I’m not saying an elevated NEFA concentration is necessarily a negative thing in the context of a low carbohydrate diet, because it's probably an adaptive mechanism, and fat oxidation also increases on low-carb. However, I think it's fair to point out that we don't have great long-term data on outcomes of this.
Low-carbohydrate diets can also substantially raise post-prandial triglycerides (as far as I know, this effect is attenuated if protein is also increased alongside the reduction in carb).
This isn’t my area of research at all, but in general (as far as I know) elevated post-prandial triglycerides increase the risk of CVD and serious CVD events. It might be the case that the reduction in fasting triglycerides following a low-carb diet cancels out the elevated post-prandial triglycerides…...
..but…you can see the uncertainty in all of this. And it seems strange to me to worry about a rise in glucose 20% above the baseline for 20-30 mins, but not worry about a similar or greater magnitude of increase in triglycerides that lasts for hours.
Adding in more saturated fat and calories just to lower glucose
I saw an advert for a personalised nutrition company that seemed to suggest the best way of dealing with “glucose spikes” from blueberries [ed. it probably wasn’t the blueberries and here’s why] was to add yoghurt to them.
Why would you do this? Firstly, this advert doesn’t tell us how they defined “glucose spike”, but I would die of shock if a handful of blueberries causes a glucose rise in a person with normoglycaemia that was anything at all to to worry about. And look, yoghurt’s a great food with tons of micronutrients, and is better than butter in terms of its effect on LDL cholesterol. But still, adding in about two tablespoons of Greek yoghurt could give you about 15% of your recommended daily intake of saturated fat. To flatten a glucose that doesn’t need flattening. It’s just nutritionally illiterate.
Avoiding foods which can improve other CVD risk markers, eg blood pressure and many other aspects of health.
Many foods which contain nutrients and phytonutrients that have favourable health impacts like lowering blood pressure also contain some carbohydrate, eg fruits, and dairy. There are multiple examples from personalised nutrition companies (and from people who these personalised nutrition companies contract to promote their products) that warn about “glucose spikes” from whole fruit, or about the glycaemic consequences of semi-skimmed milk (seriously).
And I can't highlight enough how absurd it is that people whose glucose excursions are not posing any health risk whatsoever as far as we know, are actively encouraged (by companies that are run by actual doctors) to make dietary changes which could worsen their health.
Causing people to worry unnecessarily AND SUCKING THE JOY OUT OF PEOPLE’S LIVES
So this brings me onto the last but not least downside of the use of CGM in people with normal blood glucose.
I know many people - and I have many patients - who are pretty type A. They enjoy monitoring and tracking their sleep, food, exercise and indeed glucose. These are the kind of people that can and do strictly follow a ketogenic diet, and they do it for the sole reason that it makes them feel mentally alert. And good for them. We all have our own values, and things that matter to us, and so if someone feels like a CGM is giving them a sense of control that they find valuable, crack on.
What is not ok though is that a view is being spread that people need to worry about something that they almost certainly don't need to worry about, and people are being advised to avoid foods that they might enjoy. People have enough to worry about in their daily lives anyway, and the idea that people with a perfectly normal A1c are being encouraged to use a device that takes a glucose reading every five minutes 24 hours a day to keep an eye on the foods that might be causing “glucose spikes” and “inflammation”???
Let me draw this article to a close by telling you about the patient who made me realise how just utterly wank these personalised nutrition products can be:
I have changed some details to protect the patient, but the description here reflects exactly what happened.
My patient was in her 60s, had been born in Greece and loved to share Greek culinary customs with her sons and grandsons. She had no major health concerns except a total cholesterol of 6.2mmol/L.
Her diet had always been pretty Mediterranean: with fish, lots of vegetables, lots of pulses, yoghurt, some meat, and bread. She read a newspaper article about a new science-based product that could tell her what foods she should be eating based on her unique metabolism, and she was intrigued. When she got the tests back (after paying >£500), they told her that she couldn't tolerate carbohydrates. Her HbA1c was 5.1%. Let me repeat that. Her HbA1c was 5.1%.
So she cut out most of the carbs, and ate a lot more meat and fat. And this is what caused her elevated cholesterol. She had wanted to introduce more pulses into her diet because she missed them, but when she tried, she would find her glucose would go up to a concentration she thought was too high. (Read here why a carbohydrate load causes an exaggerated glucose response following a period of relative carbohydrate restriction). And of course, this really made her anxious because she had been told that she couldn't tolerate carbohydrates.
And for the patient, this was the thing that really seemed to have the most negative impact. She told me she was miserable, anxious and confused. I took my time, and as gently as I could talked her through why she should basically just go back to what she was eating previously!!
And in a little, hopeful voice towards the end of the conversation she asked me whether it would be okay to sometimes have some bread. One of the things that she loved to do with her sons and grandsons was to bake bread the way she herself had grown up doing, and share this with her family. She had stopped doing this.
This patient is the reason I am writing this whole series.
I recently read Food for Life, whilst reading it it felt like an advert for a company. It also contained an incredible amount of opinion with out any science to back it up. Thank you for this series, I think your message is incredibly important at this time with the huge fad of CGM's.
I have been reading your articles and I think you are right that we might be confounding correlation and causality. I have always been a bit skeptical about the claim that carbs are bad because I have not seen any evidence that low carb is better for health and most evidence-based recommendations like the mediterranean diet are moderate in carbs (although I have heard multiple times that mediterranean is low carb, how can 40-50% carbs be low carb???). This recommendation, of course, does not critically asses the potential damage of high fat diets. However, what I wonder and that I cannot answer is then, what is causing this metabolic dysfunction in the first place? Lack of physical activity? Additives in food? Lack of vegetables? Nutrient deficient diets? Extreme dieting patterns (low carb or low fat)? Excess fructose? Certainly, the arrow of causality High glucose excursions=future T2D is appealing for its simplicity, and I do not know a definite answer about what is causing this disease in the first place, except a constellation of factors