Sugar crash


My recent blog post on food coma (14-Jan-2019) not only uncovered another hidden symptom in MSers but has led us to start exploring this phenomenon in our patients and, hopefully, to some evidence-based advice on how to manage the problem. 

In our short web survey on food coma, I was surprised to find that 86% of MSers report this phenomenon with 28 of the 81 respondents (35%) reporting their food coma as being severe or severe-and-incapacitating. When exploring the science I was surprised to uncover that insulin, the hormone that the pancreas releases in response to carbohydrates or sugar, is one of the main mediators of food coma. How could this be when my mother always used to accuse me of having a sugar rush as a child? A sugar rush is a so-called period of hyperactivity that occurs after ingesting too much sugar in a short period of time. 

I was therefore not surprised to read the following well-done metanalysis debunking this piece of dogma. On the contrary, sugar does not cause a sugar rush, but a sugar crash, another term for food coma. 

This and other evidence keeps mounting against sugar and the sugar industry. There seems to be very little reason for anyone to consume sugar or processed carbohydrates in any form. This is why nutritionists have started to refer to processed carbohydrates as empty calories.

So I am going to repeat myself again if you want to select a diet that is healthy for you can I suggest a real-food diet low in carbohydrates, i.e. free of all processed carbohydrates. This means you may need to get most of your calories from fats and proteins. The carbohydrates you eat on the real-food diet will be unprocessed with a low glycaemic index. As a result of this diet, you will keep your insulin levels low and hence you will reduce your postprandial hypersomnolence or ‘food coma’. 

Keeping your insulin levels low will have other positive effects on your health; i.e. it will help you maintain a healthy weight, counteract insulin resistance and hence your chances of developing the metabolic syndrome (insulin resistance, diabetes, hypertension, hyperlipidaemia and obesity) and it should reduce your risk of developing common cancers.

What is there to lose? How easy is it to stick to the real-food diet? You tell me. 

Mantantzis et al. Sugar rush or sugar crash? A meta-analysis of carbohydrate effects on mood. Neurosci Biobehav Rev. 2019 Jun;101:45-67. 

The effect of carbohydrate (CHO) consumption on mood is much debated, with researchers reporting both mood improvements and decrements following CHO ingestion. As global consumption of sugar-sweetened products has sharply increased in recent years, examining the validity of claims of an association between CHOs and mood is of high importance. We conducted a systematic review and meta-analysis to evaluate the relationship between acute CHO ingestion and mood. We examined the time-course of CHO-mood interactions and considered the role of moderator variables potentially affecting the CHO-mood relationship. Analysis of 176 effect sizes (31 studies, 1259 participants) revealed no positive effect of CHOs on any aspect of mood at any time-point following their consumption. However, CHO administration was associated with higher levels of fatigue and less alertness compared with placebo within the first-hour post-ingestion. These findings challenge the idea that CHOs can improve mood, and might be used to increase the public’s awareness that the ‘sugar rush’ is a myth, inform health policies to decrease sugar consumption, and promote healthier alternatives.

About the author

Prof G

Professor of Neurology, Barts & The London. MS & Preventive Neurology thinker, blogger, runner, vegetable gardener, husband, father, cook and wine & food lover.


  • I have had MS for 20 years or so, and feel much better in myself for having been low(ish) carb and high (healthy) fat for the past year or so. I have found this advice of the excellent Public Health Collaboration to be particularly helpful, and urge it upon anyone who will listen!

    • The following paragraph from the document is particularly relevant:

      “5. Optimum Sugar Consumption For Health is ZERO. Added sugar has no nutritional value whatsoever. There are no biochemical reactions in the human body that require dietary fructose. No single study exists that demonstrates benefit associated with its consumption. [23] Excess sugar consumption is strongly associated with increasing risk of type 2 diabetes, hypertension, and cardiovascular disease, independent of its calories or its effects on body weight [24, 25, 26]. While we welcome the recent World Health Organisation maximum LIMIT recommendations, public health messaging should emphasize the fact that sugar plays NO role in a healthy diet. Sugar should be relegated to the status of condiment or food additive, rather than food. It should return to its role as a decadent unnecessary thing to be consumed occasionally rather than a daily part of a healthy diet. In addition we recommend that food labelling on added sugar should be recorded as number of teaspoons. This enables consumers to make more informed decisions when purchasing products in the supermarket.”

  • I have “PPMS”, I don’t buy into the ant-carb hysteria – I love bread, especially homemade bread, and feel the better for including it in my diet. Also, making bread is a wonderful thing.

    But I learned about sugar crashes years and years ago – at school I think – this is not new. I avoid refined sugar, as I question the effect on the immune system and, importantly, for dental health.

    • Most peoples definition of real food includes bread, but the slow-fermented variety (sourdough). Most of the cheap bread in supermarkets is ultra-processed, for example, it contains added sugar as a starter to speed up fermentation and CO2 production and ultra-refined flour. Bread should have no added sugar; please check the label and ask why you need sugar added to your bread.

      • Another thing about sourdough is that uses a wild culture that is a mixture of bacteria and yeast, which results in the complex digestion of gluten. Most processed bread uses a monoculture (single rapidly fermenting yeast) that leaves a lot of gluten in its natural state. Some think this is one of the reasons behind the rapid increase in gluten-sensitivity in the general population.


    With two hungry males to feed alongside myself, I’ve been making use of the advice in this BBC article. Living in hope that every little thing helps, especially as I can’t resist a weeny amount of chocolate each evening.

  • “There seems to be very little reason for anyone to consume sugar or processed carbohydrates in any form.”

    How about ss(n)ri usage?
    More potent antidepressant or dosage I take, more profound urge to INTAKE CARBOHYDRATES I feel.
    And I think this is know issue, as this mentioned even in the drug leaflet.
    I feel like the Chip ‘n’ Dale‘s Monty’s

  • Oh dear. Just wait until the OMS brigade read this post. Your moderator will be working overtime 😀.

  • All food is real. What the Prof forgets here is the many socio-economic factors which may prevent people eating whatever his definition of ‘real food’ may be.

      • All well and good but we’re alive now and trying to feed 8-9 billion people with foods we ate ‘exclusively for thousands of years’ is fantasy land stuff. Not to mention the health and wealth inequalities so prevalent today.

  • I’ve been reducing carbs for a while as I found bread or heavy lunches send me to sleep. I try to eat fruit, nuts and seed plus live yoghurts in the day. Every now and then I do make a home made cake! Life needs some joys, when many things go with MS.
    I’ve noticed though that my BP drops after my evening meal even a light on carb ones. So it can go down to 90 ish over 60 ish. I assume this is part of food coma

    • A post-prandial drop in blood pressure usually indicates problems with the autonomic nervous system (ANS) THe ANS regulates blood pressure and should keep it normal after meals.

      • Thank you for your reply. I’ve recently had an ECG as my pulse also drops, nothing sinister showing so will have to chat with GP again. Is the ANS also affected by MS? This might seem obvious to some but the local neuro says it’s unusual for MS to impact on BP.

  • There’s no end of advice on diet. Try the Sadhguru. Or fast. Or this, or that.

    I follow my own instincts now.

  • One more reason to eat low glycemic foods

    Dimethyl fumarate targets GAPDH and aerobic glycolysis to modulate immunity

    Activated immune cells undergo a metabolic switch to aerobic glycolysis akin to the Warburg effect, presenting a potential therapeutic target in autoimmune disease. Dimethyl fumarate, a derivative of the Krebs cycle intermediate fumarate, is an immunomodulatory drug used to treat multiple sclerosis and psoriasis. Although its therapeutic mechanism remains uncertain, it covalently modifies cysteine residues in a process termed “succination.” Here, we show that dimethyl fumarate succinates and inactivates the catalytic cysteine of the glycolytic enzyme GAPDH both in vitro and in vivo. It thereby downregulates aerobic glycolysis in activated myeloid and lymphoid cells, which mediates its anti-inflammatory effects. Our findings provide mechanistic insight into immune modulation by dimethyl fumarate and represent a proof of concept that aerobic glycolysis is a therapeutic target in autoimmunity

    We next measured the production of IL-1β under low (0.5 mM) or high (10 mM) glucose concen-trations and found that DMF was much less effective in the presence of high glucose (Fig. 3A), suggesting that its anti-inflammatory effect can be overcome by driving glycolysis higher with saturating concentrations of glucose


    10.1126/science.aan4665 (2018).

  • I think it’s something else, healthty people eat tons of sugar and don’t have food coma. Anyway, your theory can be easily checked, somebody should compare blood sugar in ms and healthy controls after a meal. Or maybe there is such study already? I’d say that the cause is decreased blood flow after meal (because blood goes to stomach) – this can be measured too.

By Prof G



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