WIDLIMS ep #12 – We need to understand this about carbohydrates

In this week's episode, host and final year medical student Linda (she/her) discusses carbohydrates and dispels carb-phobic myths. We discuss...

• what carbohydrates are, and why ‘carbohydrates’ is a term encompassing a vast amount of foods and is not specific enough when talking about ‘cutting carbs’
• insulin resistance and diabetes – what most people misunderstand
• how insulin resistance comes about and can be reversed, including the role of dietary fat, stored fat and intramyocellular lipids
• how insulin resistance can be managed and improved, and type 2 diabetes reversed with plant-based diets high in carbohydrates (!) but low in fat, according to the science

Mentioned in the episode

Please note that all of these references are discussed in context in the article below (ca. 5 minute read).

• Fruit juice & white rice diet – read more HERE
• One high fat meal can cause insulin resistance – read more HERE
• Paper by Hall and Chung ‘Low-carbohydrate diets for the treatment of obesity and type 2 diabetes’ doi:10.1097/MCO.0000000000000470, access HERE
• DiRECT trial
• Intramyocellular lipid and diet, spillover effect and interference with insulin signaling – scroll down to read first paragraph in article below
• Population studies on benefits of consuming… and diabetes
  • healthy plant foods – read more HERE
  • whole grains – read more HERE
  • fruits and vegetables – read more HERE
• Legumes and the second meal effect – read more HERE
• The PURE study and rebuttals – see references in paragraph tiled ‘PURE study’ below
• Benefits of vegetarian and vegan diets in insulin control – see references 22-27 below or the first bullet point in further reading!

Further reading

• An excellent general paper summarising plant-based diets and insulin resistance mechanisms in general, with lots of further references too
  • McMacken M, Shah S. A plant-based diet for the prevention and treatment of type 2 diabetes. J Geriatr Cardiol. 2017;14(5):342-354. doi:10.11909/j.issn.1671-5411.2017.05.009
  • Available HERE
• Mastering Diabetes. Insulin Resistance Diet – What to eat and why. Lecture available on YouTube HERE with corresponding blog post (time stamps, references) HERE
  • If you are struggling to understand how the glucose-insulin model without acknowledging the interference of lipids in the pathway, I would strongly recommend watching this lecture
  • Mastering Diabetes was founded by Cyrus and Robbie, two people with type 1 diabetes who are incredibly knowledgeable about the science around insulin resistance. They have also managed to improve their own insulin sensitivity and run seminars and classes, they also recently released a book I have yet to read.
• How not to die and How not to diet by Michael Greger (MD), founder of Nutritionfacts.org – there are chapters discussing diabetes and diet
• Body in Balance by Neal Barnard (MD), again with a discussion of low fat whole food plant-based diets and glycaemic control
• Plant-Based Health Professionals UK – Plant-based diets in the prevention and treatment of type 2 diabetes – HERE
• The Exam Room Podcast – episode on ‘bad’ carbs vs ‘good’ carbs – listen HERE

Carbohydrates: friend or foe?

Quite obviously, the answer to this is NOT foe! Carbohydrates are one of the macronutrient groups, i.e. one of the larger components of food (the other two are proteins and fats). All foods contain carbohydrates, protein and fat but in varying proportions.

Typically, most higher carbohydrate foods are labelled as ‘carbs’ and often included under one big umbrella. However, that is oversimplifying things hugely, to the detriment of many people’s health. Just like there are better and worse forms of protein and fat, carbohydrate quality is critical to deciding whether a food is healthful or not so healthful.

I am writing this article, and recording this Solo Sunday short episode, because I am incredibly tired and frustrated of all carbohydrates being treated the same, and demonised widely in our society: from the doctor’s and dietician’s office, to the red carpet, to social media, to social events!

Repeat after me:

• we need to stop demonising carbohydrates!
• carbohydrates can be healthy or less healthy depending on the quality of the source and type of food
• carbohydrates will not automatically give you diabetes!
• carbohydrates are not the main driver behind insulin resistance!

This article will cover some of the main arguments for eating carbohydrates, and against cutting them out and replacing them with other less healthy sources of food. Remember, I advocate for a plant-heavy diet, a whole foods plant-based diet, based on vegetables, fruits, whole grains, legumes, nuts, seeds and water. This is what time and time again has been shown to be most healthful (1).

Fears about carbohydrates, weight and diabetes

Understanding physiological glucose, insulin and lipid interplay

I am not going to lie, I cannot remember much from our metabolism teaching in first year: I know there were many diagrams about glucose and lipid metabolism, and possibly something about lipids interfering with how glucose behaves in the body. What I do know though, is how demonised carbohydrates are in mainstream media, and also in medicine. Low carbohydrate diets have come up time and time again, and I have listened to patients and healthcare professionals discussing ‘cutting carbs’, and I have heard many a diabetic (and non-diabetics) fear fruit.

So let us go back to some basics.

The main energy source for the various processes that take place in our living, breathing bodies, is glucose – this is what is measured during what some would simply call a ‘blood sugar test’. Blood glucose can be taken as a snapshot, or it can be measured as the HBA_1C which is a marker of glucose blood levels over about 3 months (it is related to how it binds with haemoglobin in the body).

There are several different types of diabetes mellitus, but the best known ones are type 1 and type 2. Type 1 cannot be reversed, as it involves the pancreas failing to produce insulin. Type 2 (hereafter referred to as T2DM) involves a progressive insulin resistance, and may ultimately lead to complete failure of the body to respond to and produce endogenous insulin, meaning a person with longstanding T2DM may go on to need insulin injections, just as a person with T1DM does. We are concerned about diabetes, as it involves having high levels of blood glucose, which is damaging to blood vessels, causing complications such as kidney disease, poor wound healing, blindness and the need for limb amputations.

Our blood glucose levels are however influenced by many different things.

Enter insulin.

Insulin is a hormone with many effects in the body, but its primary role as far as we are concerned for this discussion, is that insulin acts as a signaling molecule to facilitate glucose entering our various cells in the body, so that it can be used for energy. Insulin is often compared to being a ‘key’, unlocking the ‘key hole’ in a cell, to let the glucose in.

When we eat a meal, our body will respond by releasing insulin so that our cells can use it to ‘unlock’ and take in glucose for use.

Therefore, the rhetoric often goes, eating a carbohydrate-rich meal will cause a large spike in insulin. It is not good to have high insulin levels, as it acts as an anabolic hormone and exerts many other effects in the body, as previously mentioned.

Many diabetics are told to reduce their carbohydrate consumption. If they eat meals containing little to no carbohydrates, their blood glucose level will go up less and their body will release less insulin.

Many who follow a low carbohydrate diet, will lose weight, and will appear to ‘reverse’ their diabetes and come off medication (2).

But… following a low carbohydrate diet in order to ‘reverse’ diabetes is a bit of an illusion. The marker of diabetes is high blood glucose, and if we avoid consuming carbohydrate-rich foods (containing glucose), we are avoiding the symptom of diabetes. But diabetes is not caused by eating too much sugar. There literally was a study in the early 1900s where participants reversed their T2DM by eating a diet consisting of white rice and fruit juice! (3) Diabetes is driven by increased insulin resistance, and poor sensitivity to insulin. Low carbohydrate diets do not reduce insulin resistance or improve insulin sensitivity per se. Consuming just one high-fat meal can still cause increased insulin resistance, despite low or no carbohydrate content, as demonstrated in one study where subjects were given palm oil, for example (4).

If a patient has been on a low carbohydrate diet, and then consumes a food with a higher carbohydrate content, they will still have that large spike in both glucose and insulin. They have thus not reversed their diabetes, they are simply masking their symptoms. Reintroducing carbohydrates is falsely mistaken for triggering the condition again, when the truth is that the driving forces behind the diabetes never truly went away! Insulin sensitivity reduces on a low carbohydrate, high fat diet and insulin sensitivity improves on a diet which is high in carbohydrates and proportionally lower in fat (5). Not only does a low carbohydrate not actually treat and reverse diabetes, it can be very dangerous for cardiovascular health, especially if high in animal products and saturated fats (6).

This conclusion from a paper by Hall and Chung again reiterates how low carbohydrate diets can appear successful in the short term – though insulin sensitivity and how the body is able to respond to carbohydrate-rich foods is in fact impaired (7).

Glycemic control and hyperinsulinemia are improved by low-carbohydrate diets, but insulin sensitivity and glucose-stimulated insulin secretion may be impaired, especially in the absence of weight loss.

From Hall KD, Chung ST. Low-carbohydrate diets for the treatment of obesity and type 2 diabetes. Curr Opin Clin Nutr Metab Care. 2018;21(4):308-312. doi:10.1097/MCO.0000000000000470 Available here

So what actually drives insulin resistance, and is the root cause we must address if wanting to manage or even reverse type 2 diabetes mellitus?

We know that significant weight loss in obese patients with T2DM can cause remission of T2DM and improve blood markers; this is weight lost by any means, such as through severe calorie restriction, or by following a low carbohydrate diet (2,8,9).

The real culprit here, or at least what we should be concerned about, is intramyocellular lipid – IMCL – fat stored within skeletal muscle cells. The carbohydrate-insulin model is not completely accurate, as we know that lipids interfere with the signaling pathway, and to completely ignore that is simply not scientifically accurate (9,10).

It is a diet high in fat, or any diet with a significantly positive calorie balance over time leading to increased body weight and lipid accumulation, which drives insulin resistance. As lipid (fat) accumulates in not only adipocytes (fat cells), but also in other locations such as muscle and liver cells, and is deposited in general and even spills out into the blood stream (the ‘spillover’ effect), the normal insulin signaling pathway is disrupted (11, 12).

Also, typically foods that are deemed to be high in ‘sugar’ are often high in the culprit, fat! Think of a cookie: it has sugar, yes, but also butter in it. Potato chips: again carbohydrate-rich, but also deep fried and high in fat.

So no, carbohydrates are not the main concern. Of course it is not good to be eating lots of sugary processed foods, or eating in a vast energy excess – but nobody is claiming that! I am simply asking you to stop fearing whole, carbohydrate rich foods.

Wholesome carbohydrates, consumed ad libitum are not dangerous, and not to be avoided!

The PURE study

You may have seen the now famous TIME cover stating ‘Butter is Back!’, or various magazines and online clickbait articles telling you why saturated fat is not something to be avoided, while carbohydrates are slandered. A few years ago, in 2017, the PURE study was published (18). It claimed that low fat diets high in carbohydrates were associated with higher mortality, and that high fat diets did not have any negative impact on health. It was a very large study, which hit many media headlines.

BUT it was not perfectly designed. There were many flaws with it, such as that it grouped all carbohydrates together (white rice is not the same as brown rice, or rice krispies) and did not take into account socioeconomic status, among other things (19,20).

Benefits of high quality carbohydrate consumption

We know that those living the longest, healthiest, lives in the world are not avoiding carbohydrates. In the so-called ‘Blue Zones’, whole food carbohydrate sources are consumed in abundance as part of largely plant-based diets (13). Research has shown that high consumption of fruits, vegetables and whole grains is beneficial for health, and not associated with diabetes (14,15,16). And let us not forget about legumes/pulses, which honestly deserve an entire episode of their own: beans, peas, lentils… They have amazing health benefits, and have something called the ‘second meal effect’, where eating beans at dinner, for example, can influence your metabolism for the next day still (at your second meal)! They are able to lower blood glucose levels, have a low glycaemic index and are appetite-suppressing (17). Legumes are also a great source of plant protein, but are also fairly high in carbohydrates depending on which one you choose. Imagine missing out on all those health benefits just because of trying to (needlessly) ‘cut carbs’! The horror!

So okay, we know that consuming foods high in carbohydrates – because remember, even though potatoes or quinoa or apples are often labelled as ‘carbs’ they do contain both protein and fat, although in varying proportions – is good depending on the quality of the carbohydrate. Baked or boiled potatoes? Fabulous! Deep fried potato chips? Not so much.

And where do plant-based diets come into this?

I already mentioned how evidence from the Blue Zones favours diets high in whole plant foods. Vegetarian and vegan diets have also been associated with lower intramyocellular lipids, better insulin sensitivity, lower insulin resistance and lower rates of type 2 diabetes (21–24). They can also be used as a therapeutic intervention to reverse diabetes. Some amazing patient accounts can be found via Plant-Based Health Professionals UK or Forks Over Knives. High carbohydrate diets based on whole foods are also naturally high in fibre, which has amazing benefits for our gut microbiomes and helps with satiety and again blood sugar levels. It is hard to feel restricted on a whole food plant-based diet, as you can eat to your satiety level (and beyond!) without any issues in terms of weight gain or health (25). These beneficial effects on glycaemia were observed even without actual weight loss too, though (26,27).

Further evidence to support this has been observed in the Adventists’ Health studies and the Nurses Health studies for example.

The evidence is clear: a whole-food plantbased diet, naturally high in carbohydrates and lower in fat is good for you!

A note on restricting fat and ‘bad’ foods

Weight loss has been known to improve some health outcomes such as T2DM as described above. And it would appear that diets specifically low in fat are best for cardiovascular health outcomes (truly low fat is with about 20% of calories from fat).

However, I want to mention that there is absolutely no point in losing weight if it is done in an unsustainable way. Furthermore, weight loss should not be a primary goal but rather incorporating more healthy habits into our daily routines.

I also do not believe in rigid food rules and restriction. If you want to have some vegan ice cream, french fries, donuts and chocolate despite these foods often being classed as ‘bad’ due to being highly processed etc – HAVE THESE FOODS! Again, restriction will not help you in the long term and may lead to eating disorders. This has been discussed in episodes 4 and 5 of WIDLIMS, so I would highly recommend checking out the shownotes for those.

• Episode 4 – the secret to lasting behaviour change CLICK HERE
• Episode 5 – weight management: have we got it wrong? CLICK HERE

Final thoughts

I used to believe that carbohydrates, including potatoes and mangoes, were the devil. I used to follow a low carbohydrate diet and initially saw good results from it… until I didn’t!

I hope that this article, and this podcast episode has helped you understand our carbohydrate metabolism a bit better. It is my wish for you to understand how crucial carbohydrates are to our health and normal functioning, and to not advocate for fad diets for yourself or future patients. I want you to consider the quality of carbohydrates, and of the diet in general, aiming for the optimal whole food plant-based diet most of or all of the time!

If you have any further questions, I would be happy to answer them. Contact me on here, in the comments, via my contact form or online @widlims on Instagram or Twitter.

I would love to hear from you!

REFERENCES

1) Katz DL, Meller S. Can we say what diet is best for health?. Annu Rev Public Health. 2014;35:83-103. doi:10.1146/annurev-publhealth-032013-182351 Available at: https://www.annualreviews.org/doi/full/10.1146/annurev-publhealth-032013-182351

2) Hallberg SJ, McKenzie AL, Williams PT, et al. Effectiveness and Safety of a Novel Care Model for the Management of Type 2 Diabetes at 1 Year: An Open-Label, Non-Randomized, Controlled Study [published correction appears in Diabetes Ther. 2018 Mar 5;:]. Diabetes Ther. 2018;9(2):583-612. doi:10.1007/s13300-018-0373-9

3) KEMPNER W, PESCHEL RL, SCHLAYER C. Effect of rice diet on diabetes mellitus associated with vascular disease. Postgrad Med. 1958;24(4):359-371. doi:10.1080/00325481.1958.11692236 https://nutritionfacts.org/2016/08/16/introducing-the-kempner-rice-diet/

4) Hernández EÁ, Kahl S, Seelig A, et al. Acute dietary fat intake initiates alterations in energy metabolism and insulin resistance. J Clin Invest. 2017;127(2):695-708. doi:10.1172/JCI89444 https://pubmed.ncbi.nlm.nih.gov/28112681/

5) Himsworth HP. Dietetic factors influencing the glucose tolerance and the activity of insulin. J Physiol. 1934;81(1):29-48. doi:10.1113/jphysiol.1934.sp003113 Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1394223/

6) https://nutritionfacts.org/2016/11/22/how-a-low-carb-diet-is-metabolically-like-being-obese/

7) Hall KD, Chung ST. Low-carbohydrate diets for the treatment of obesity and type 2 diabetes. Curr Opin Clin Nutr Metab Care. 2018;21(4):308-312. doi:10.1097/MCO.0000000000000470 https://pubmed.ncbi.nlm.nih.gov/29677013/

8) https://www.directclinicaltrial.org.uk/Pubfiles/Low-calorie%20diets%20in%20the%20management%20of%20type%202%20diabetes%20mellitus.pdf

9) Hall KD, Chen KY, Guo J, et al. Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men. Am J Clin Nutr. 2016;104(2):324-333. doi:10.3945/ajcn.116.133561 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4962163/

10) Kuhlmann J, Neumann-Haefelin C, Belz U, et al. Intramyocellular lipid and insulin resistance: a longitudinal in vivo 1H-spectroscopic study in Zucker diabetic fatty rats. Diabetes. 2003;52(1):138-144. doi:10.2337/diabetes.52.1.138 Availalbe via: https://diabetes.diabetesjournals.org/content/52/1/138

11) Muoio, D.M. Revisiting the connection between intramyocellular lipids and insulin resistance: a long and winding road. Diabetologia 55, 2551–2554 (2012). https://doi.org/10.1007/s00125-012-2597-y https://link.springer.com/article/10.1007/s00125-012-2597-y#citeas

12) https://nutritionfacts.org/video/the-spillover-effect-links-obesity-to-diabetes/

13) https://www.bluezones.com/recipes/food-guidelines/ see also https://www.nationalgeographic.com/magazine/2020/01/these-traditional-diets-from-the-blue-zones-can-lead-to-long-lives-feature/

14) Cooper AJ, Forouhi NG, Ye Z, et al. Fruit and vegetable intake and type 2 diabetes: EPIC-InterAct prospective study and meta-analysis. Eur J Clin Nutr. 2012;66(10):1082-1092. doi:10.1038/ejcn.2012.85

15) BMJ 2020;370:m2206 https://www.bmj.com/content/370/bmj.m2206

16) BMJ 2020;370:m2194 https://www.bmj.com/content/370/bmj.m2194

17) Mollard RC, Wong CL, Luhovyy BL, Anderson GH. First and second meal effects of pulses on blood glucose, appetite, and food intake at a later meal. Appl Physiol Nutr Metab. 2011;36(5):634-642. doi:10.1139/h11-071 https://pubmed.ncbi.nlm.nih.gov/21957874/

18) The PURE study in the Lancet. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(17)32252-3/fulltext

19) https://www.hsph.harvard.edu/nutritionsource/2017/09/08/pure-study-makes-headlines-but-the-conclusions-are-misleading/

20) https://plantbasedhealthprofessionals.com/the-pure-study-low-fat-diets-increase-risk-of-death

21) Goff, L., Bell, J., So, P. et al. Veganism and its relationship with insulin resistance and intramyocellular lipid. Eur J Clin Nutr 59, 291–298 (2005). https://doi.org/10.1038/sj.ejcn.1602076 https://www.nature.com/articles/1602076#citeas

22) Kahleova H, Pelikanova T. Vegetarian Diets in the Prevention and Treatment of Type 2 Diabetes. J Am Coll Nutr. 2015;34(5):448-458. doi:10.1080/07315724.2014.976890

23) Trapp CB, Barnard ND. Usefulness of vegetarian and vegan diets for treating type 2 diabetes. Curr Diab Rep. 2010;10(2):152-158. doi:10.1007/s11892-010-0093-7 https://pubmed.ncbi.nlm.nih.gov/20425575/

24) Barnard ND, Cohen J, Jenkins DJ, et al. A low-fat vegan diet and a conventional diabetes diet in the treatment of type 2 diabetes: a randomized, controlled, 74-wk clinical trial. Am J Clin Nutr. 2009;89(5):1588S-1596S. doi:10.3945/ajcn.2009.26736H https://pubmed.ncbi.nlm.nih.gov/19339401/

25) Anderson JW, Ward K. High-carbohydrate, high-fiber diets for insulin-treated men with diabetes mellitus. Am J Clin Nutr. 1979;32(11):2312-2321. doi:10.1093/ajcn/32.11.2312 https://pubmed.ncbi.nlm.nih.gov/495550/

26) Olfert MD, Wattick RA. Vegetarian Diets and the Risk of Diabetes. Curr Diab Rep. 2018;18(11):101. Published 2018 Sep 18. doi:10.1007/s11892-018-1070-9 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6153574/

27) McMacken M, Shah S. A plant-based diet for the prevention and treatment of type 2 diabetes. J Geriatr Cardiol. 2017;14(5):342-354. doi:10.11909/j.issn.1671-5411.2017.05.009 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5466941/