Margaret McCartney: Promising miracle diet fixes isn’t fair on anyone
BMJ 2017; 358 doi: https://doi.org/10.1136/bmj.j4226 (Published 25 September 2017) Cite this as: BMJ 2017;358:j4226
All rapid responses
Rapid responses are electronic comments to the editor. They enable our users to debate issues raised in articles published on bmj.com. A rapid response is first posted online. If you need the URL (web address) of an individual response, simply click on the response headline and copy the URL from the browser window. A proportion of responses will, after editing, be published online and in the print journal as letters, which are indexed in PubMed. Rapid responses are not indexed in PubMed and they are not journal articles. The BMJ reserves the right to remove responses which are being wilfully misrepresented as published articles or when it is brought to our attention that a response spreads misinformation.
From March 2022, the word limit for rapid responses will be 600 words not including references and author details. We will no longer post responses that exceed this limit.
The word limit for letters selected from posted responses remains 300 words.
Well-controlled studies with substantial carbohydrate restriction (5-20%kcal from carbohydrate) demonstrate that when individuals with type 2 diabetes do stick to a low-carbohydrate diet, the reduction in post-prandial glucose concentrations can be impressive, and clinically important (1). Moreover, significant improvements in HbA1c, glucose variability (likely through reductions in post-prandial excursions) and the lipid profile can occur with a low-carbohydrate diet in the absence of or independent of weight loss (1-3). The former is not true of any other dietary approach I am aware of. This may be very attractive to people with type 2 diabetes, along with other potential benefits including a reduced need for medications (2-4). ). I believe the role of a healthcare practitioner includes laying out the options and clearly identifying (any) risks and possible benefits, and what the diet itself would look like. The patient themselves can then make an informed choice. The current status quo of “long-term trials show no difference” conflates physiological efficacy and long-term adherence. However, Dr McCartney is right that there are many unanswered questions which are currently barriers to practitioners who want to give genuine evidence-based advice.
In particular, the exact cut-off of carbohydrate intake below which these diets are effective (5), and the impact of the replacing macronutrient or food is not currently clear. This cannot be established from the literature where substantial weight loss (>6% weight loss) observed in many of the low-carbohydrate studies is a confounding factor (2,4) Indeed, a very-low-calorie diet with 46% of calories from carbohydrate (of which the majority were monosaccharides) created headlines when it was shown to normalise beta-cell function, restore euglycaemia and increase hepatic and peripheral insulin sensitivity in people with type 2 diabetes (6). Additionally, the studies which demonstrate substantial reductions in glucose concentrations in the absence of or independent of weight loss replace the carbohydrate with a substantial amount of protein (~30%kcal from protein) (1-3), which itself has been linked to improved insulin secretion and reduced post-prandial glucose concentrations (7,8). In short, it is not clear whether the impressive results observed in primary care using low-carbohydrate diets in a self-selected group of patients (9) are due to the weight loss, additional protein, or the carbohydrate-restriction.
The importance of establishing a cut-off for low-carbohydrate diets is shown by studies in which moderate reduction of carbohydrate does not cause a clinically-relevant reduction in glucose concentrations (10,11) and its replacement with foods high in saturated fat can raise LDL-cholesterol, substantially in some people (12,13). It may be the case that the LDL-cholesterol-raising effect of saturated fat does not occur when carbohydrate is reduced below a certain intake (14) but again the cut-off at which this occurs is not clear. I would worry about giving blanket advice to individuals with type 2 diabetes to restrict carbohydrates and replace with any other type of food or food group without some clarity on these issues.
The common questions I hear from other healthcare professionals about the use of low-carbohydrate diets in the management of type 2 diabetes include “what actual advice can I give?”, “what would a meal plan look like?”. I think it’s clear from the above that “Just reduce carbs” is not robustly supported by evidence. Nonetheless, there are convincing physiological reasons why a low-carbohydrate diets (with a clearly established cut-off) could be the most efficacious dietary approach – in those who enjoy and can follow this type of diet – in the management of type 2 diabetes (1-3, 15-16). I encourage our colleagues in primary care to work with academic partners to answer some of the remaining questions. We can then communicate with patients and the public with more clarity about the many potential benefits of these diets, with any risks taken into account too.
1. Gannon MC, Nuttall FQ. Effect of a high-protein, low-carbohydrate diet on blood glucose control in people with type 2 diabetes. Diabetes. 2004 Sep;53(9):2375-82 (high protein)
2. Tay J, Luscombe-Marsh ND, Thompson CH, et al. Comparison of low- and high-carbohydrate diets for type 2 diabetes management: a randomized trial. Am J Clin Nutr 2015; pii: ajcn112581. [Epub ahead of print] (High protein)
3. Mayer SB, Jeffreys AS, Olsen MK, et al. Two diets with different haemoglobin A1c and antiglycaemic medication effects despite similar weight loss in type 2 diabetes. Diabetes Obes Metab 2014; 16:90–93.
4. Yancy WS Jr, Foy M, Chalecki AM, Vernon MC, Westman EC. A low-carbohydrate, ketogenic diet to treat type 2 diabetes. Nutr Metab (Lond). 2005;2:34.
5. Snorgaard O, Poulsen GM, Andersen HK, Astrup A. Systematic review and meta-analysis of dietary carbohydrate restriction in patients with type 2 diabetes. BMJ Open Diabetes Research and Care. 2017 Feb 1;5(1):e000354.
6. Lim EL, Hollingsworth KG, Aribisala BS, Chen MJ, Mathers JC, Taylor R. Reversal of type 2 diabetes: normalisation of beta cell function in association with decreased pancreas and liver triacylglycerol. Diabetologia. 2011;54(10):2506-14.
7. Kitabchi AE, McDaniel KA, Wan JY, Tylavsky FA, Jacovino CA, Sands CW, Nyenwe EA, Stentz FB. Effects of high-protein versus high-carbohydrate diets on markers of β-cell function, oxidative stress, lipid peroxidation, proinflammatory cytokines, and adipokines in obese, premenopausal women without diabetes a randomized controlled trial. Diabetes care. 2013;36(7):1919-25.
8. Spiller GA, Jensen CD, Pattison TS, Chuck CS, Whittam JH, Scala J. Effect of protein dose on serum glucose and insulin response to sugars. Am J Clin Nutr. 1987 Sep;46(3):474-80.
9. Unwin D, Unwin J. Low carbohydrate diet to achieve weight loss and improve HbA1c in type 2 diabetes and pre‐diabetes: experience from one general practice. Practical Diabetes. 2014 Mar 1;31(2):76-9.
10. Wolever TM, Mehling C. Long-term effect of varying the source or amount of dietary carbohydrate on postprandial plasma glucose, insulin, triacylglycerol, and free fatty acid concentrations in subjects with impaired glucose tolerance. Am J Clin Nutr. 2003;77(3):612-21.
11. Larsen RN, Mann NJ, Maclean E, Shaw JE. The effect of high-protein, low-carbohydrate diets in the treatment of type 2 diabetes: a 12 month randomised controlled trial. Diabetologia. 2011;54(4):731-40.
12. Brinkworth GD, Noakes M, Buckley JD, Keogh JB, Clifton PM. Long-term effects of a very-low-carbohydrate weight loss diet compared with an isocaloric low-fat diet after 12 mo. Am J Clin Nutr. 2009 Jul;90(1):23-32.
13. Nordmann AJ, Nordmann A, Briel M, Keller U, Yancy WS Jr, Brehm BJ, Bucher HC. Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors: a meta-analysis of randomized controlled trials. Arch Intern Med. 2006;166(3):285-93. Review.
14. Volek JS, Sharman MJ, Forsythe CE. Modification of lipoproteins by very low-carbohydrate diets. J Nutr. 2005 Jun;135(6):1339-42. Review.
15. Allick G, Bisschop PH, Ackermans MT, Endert E, Meijer AJ, Kuipers F, Sauerwein HP, Romijn JA. A low-carbohydrate/high-fat diet improves glucoregulation in type 2 diabetes mellitus by reducing postabsorptive glycogenolysis. J Clin Endocrinol Metab. 2004;89(12):6193-7.
16. Noakes M, Foster PR, Keogh JB, James AP, Mamo JC, Clifton PM. Comparison of isocaloric very low carbohydrate/high saturated fat and high carbohydrate/low saturated fat diets on body composition and cardiovascular risk. Nutr Metab (Lond). 2006 Jan 11;3:7.
Competing interests: I have received grant funding from the Medical Research Council, Diabetes UK and the National Obesity Forum; and fellowship funding from Diabetes UK, the Winston Churchill Memorial Trust and the American Overseas Dietetics Association.
In support of the points made by George D. Henderson I would add that the correct definitions set by Feinman et al (1) are <130g carbohydrate per day for a low-carb diet and 20-50g carbohydrate per day for very-low-carb diet. This means that the 2017 meta-analysis that McCartney cites is not relevant, as it incorrectly defines low-carb as <45% of total calories from carbohydrates.
With that in mind the most recent meta-analysis between correctly defined low-carb and low-fat for weight loss was published in December 2015 by Mansoor et al (2), this is not cited by McCartney. They found that "Compared with subjects on low-fat diets, subjects on low-carbohydrate diets experienced significantly greater weight loss, greater triglycerides reduction and greater increase in HDL-cholesterol after 6 months to 2 years of intervention."
Also, the most recent and relevant meta-analysis was published in July 2017 by Meng et al (3), this was also not cited by McCartney. It concluded that "The results suggested a beneficial effect of LCD intervention on glucose control in patients with type 2 diabetes. The LCD intervention also had a positive effect on triglycerides and HDL cholesterol concentrations, but without significant effect on long term weight loss." Although this meta-analysis showed that in the long term those living with type 2 diabetes didn't lose any more weight than each other, the end result was that individuals following a low-carb diet do become healthier with better glucose control than those following a low-fat diet.
I agree that low-carb isn't a ‘miracle diet’ but surely given that starchy carbohydrates digest down into sugar, and no-one is suggesting sugar itself is a good food for someone living with type 2 diabetes, a lower carb diet is a logical dietary option. An option which does now have a reasonable evidence base.
1) Feinman, Richard D. et al. Dietary carbohydrate restriction as the first approach in diabetes management: Critical review and evidence base Nutrition , Volume 31 , Issue 1 , 1 – 13 http://www.nutritionjrnl.com/article/S0899-9007(14)00332-3/fulltext#sec2
2) Mansoor, N., et al. (2016). Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: A meta-analysis of randomised controlled trials. British Journal of Nutrition, 115(3), 466-479. doi:10.1017/S0007114515004699 https://doi.org/10.1017/ S0007114515004699
3) Meng, Yan et al. (2017)Efficacy of low carbohydrate diet for type 2 diabetes mellitus management: A systematic review and meta-analysis of randomized controlled trials. Diabetes Research and Clinical Practice , Volume 131 , 124 - 131 http://dx.doi.org/10.1016/j.di abres.2017.07.006
Competing interests: No competing interests
Readers,
Why are low-carbohydrate, high-fat (LCHF) diets that doctors across the western world used to cure (type 2) diabetes in 1923 not in 2017 still the most-effective approach for curing type 2 diabetes?
Has the human body changed so much in just a century that this once-highly effective approach no longer works?
No. The problem appears to be that doctors and public-health careerists today know less about curing type 2 diabetes than was widely known a century ago.
Reference:
pp. 2-5 http://www.australianparadox.com/pdf/Expanded-Letter-HealthDept-type2dia...
Regards,
Rory
Competing interests: No real conflicts. But full disclosure: owns a cattle station in northern Australia; owns no cattle.
Low carb and high fat and any of its permutation are meaningless terms. People do not eat carbohydrates, but food high in sugar/s, starch, and fibre/s, the three distinctly different major chemical/nutrient subgroups within carbohydrates. Besides these three subgroups are not unique with some sugars (polyols and lactose in some people) and starch (resistant starch) acting like fibres in that they are not fully digested in the upper intestinal tract.
So what is a low carb diet – one low in sugars (sucrose, fructose, or glucose, …), in starch, or in fibre/s? Or in all three and then in what proportion? And how much is low? 10%, 20%, 45% of daily calorie intake? This question also applies to high fat. Is it 10%, ≥ 40%, or any number in between. 10% is nearly double what the Japanese farmers in the famous Ancel Keys Seven Countries Study were estimated to be eating when they were found to have the lowest prevalence of cardio-vascular disease and 30% is what used to be considered optimal in the USA.
Competing interests: No competing interests
At the present time, if someone is diagnosed with diabetes in a hospital, they are likely to be fed more, not less, carbohydrate, mainly from processed starch, and less fat than they were eating before. Where is the evidence base for this recommendation? When my colleagues and I reviewed very low carbohydrate diets in diabetes for the New Zealand Medical Journal we found no evidence that higher-carbohydrate diets were tested against anything other than slightly less high carbohydrate diets before they were introduced.[1] We also affirmed that the definitions of low carbohydrate and very low carbohydrate diets proposed by Feinman et al, are valid cut-offs relating to confirmed metabolic effects.
By claiming that there is inadequate evidence for low carbohydrate diets, Margaret McCartney risks supporting a system for which there is less evidence, and a less excusable absence of evidence.
McCartney fails to cite the Kirk et al meta-analysis, which gives most detail about the metabolic effects of carbohydrate restriction in diabetes and should be used to interpret the other studies.[2] Longer studies and studies with higher carb "low carb" diets show weaker effects, but this is not because of declining efficacy in those using the low-carbohydrate diet; as studies with high compliance show, the opposite is true; the higher the adherence, the greater the benefit of the low carb approach.[3] We do not judge the clinical efficacy of drugs by what happens when people do not take them, and the sad fact is that people have not been well-supported to adhere to low carb diets in the past. They have been advised to increase carbohydrate for "maintenance", told they "need" carbohydrates from grains for various spurious reasons, told to restrict animal fats and use unpalatable oils and spreads unnecessarily, and exposed to persuasive advertising and scare stories in the media, All these shibboleths formerly undermined diet adherence, and have only been removed by the groundswell of support for low carb that concerns McCartney.
McCartney ignores a sizable body of knowledge from well-designed experiments such as those of Gannon and Nuttall showing a dose-dependent benefit of carbohydrate restriction,[4,5] Yet even with the state of knowledge she supposes, no-one should have to fight to receive a very low carbohydrate diet when in hospital or from a treatment provider; it seems clear even from McCartney's account that this should be among the options provided as soon as the risk of diabetes is identified.
What is unfair is that the most effective option is either not being offered to patients, or is not being supported in its most effective and palatable form, because a competing idea was elevated to prominence decades ago without proper testing. If the introduction of the low-fat, saturated-fat restricted diet concept had improved the treatment of diabetes, especially given accompanying improvements in early diagnostics, medication, and monitoring, then its application in the early stages of the disease, and across the population, should have seen the incidence of diabetes and rates of complications decrease.
This is the exact opposite of what has happened.
references
[1] Schofield GM, Henderson G, Thornley S, Crofts C. Very low-carbohydrate diets in the management of diabetes revisited. N Z Med J. 2016 Apr 1;129(1432):67-74.
https://www.nzma.org.nz/journal/read-the-journal/all-issues/2010-2019/20...
[2] Kirk JK, Graves DE, Craven TE, et al. Restricted-carbohydrate diets in patients with type 2 diabetes: a meta-analysis. J Am Diet Assoc. 2008;108:91- 100.
[3] McKenzie AL, Hallberg SJ, Creighton BC, Volk BM, Link TM, Abner MK, Glon RM, McCarter JP, Volek JS, Phinney SD
A Novel Intervention Including Individualized Nutritional Recommendations Reduces Hemoglobin A1c Level, Medication Use, and Weight in Type 2 Diabetes
JMIR Diabetes 2017;2(1):e5. DOI: 10.2196/diabetes.6981
[4] Nuttall FQ, Almokayyad RM, Gannon MC. Comparison of a carbohydrate-free diet vs. fasting on plasma glucose, insulin and glucagon in type 2 diabetes. Metabolism. 2015 Feb;64(2):253-62. doi: 10.1016/j.metabol.2014.10.004. Epub 2014 Oct 8.
[5] Gannon MC, Nuttall FQ. Control of blood glucose in type 2 diabetes without weight loss by modification of diet composition. Nutrition & Metabolism. 2006;3:16. doi:10.1186/1743-7075-3-16.
Competing interests: No competing interests
I agree with Dr McCartney's statement that "...there isn't one big, miracle diet fix." However, I am concerned with the discussion of some of the evidence referenced. Dr McCartney notes that an Australian trial comparing low-carb and low fat diets did not show statistically significant differences between the arms. But she also cites a study which did find a statistically significant difference (a meta-analysis in the Lancet), and immediately discounts the findings as "...surely not clinically significant."
In an article warning against using anecdotes as a basis for changing practice this is not good enough. A peer-reviewed study is being discounted here with an undefined term that has face validity ('clinically significant') but unsubstantiated scientific validity. This is exactly the way that the nutritional world's "big claims" the article rails against, gain traction in the first place.
To quote Dr McCartney, "...doctors, researchers and guideline committees can surely aspire to do better."
Competing interests: No competing interests
Re: Margaret McCartney: Promising miracle diet fixes isn’t fair on anyone
I thank the correspondents for their responses.
The paper Guess cites as showing an improvement in type 2 diabetes control was of 8 men over 5 weeks: we need better research to know what to recommend to people in general and to individuals in particular. Many trials of dietary interventions have had a notable rate of people being less adherent to dietary restrictions over time and I agree that partnership to reduce uncertainties is the best way to improve the advice we are able to give.
I disagree with Feltham regarding the definition of low carb diets: I don't think there is any agreement within the research community (or commercial diet sector) about what this means, as a brief search of the literature shows. The Mansoor meta analysis found a 2kgs weight loss advantage with low carb versus low fat diets but an increase in LDL cholesterol. In the Meng study, the effect on Hb1ac was a WMD of -0.44, which is of disputed clinical efficacy. I do agree with him though that low carb diets are no miracle, and I would hope that he is open to supporting high quality trials which are best able to untangle the substantial uncertainties remaining.
Henderson cites the Kirk meta analysis, which used short term studies with small numbers of participants, and which had high drop out rates and concluded that "Randomized, controlled studies of restricted-carbohydrate diets in patients with diabetes need to be conducted in order to evaluate the overall sustainability of outcomes and long-term safety." As I stated in the article, I agree with much of the criticism about current UK dietary guidelines, but I do not want to repeat the mistakes of the past. I appreciate that many people have done well on low carbohydrate diets, but I am also aware of others who have not.
McGovern says that I am not good enough in discerning clinical from statistical significance. Apologies: the use of the the word 'surely' I think conveys that it is my opinion that a difference in weight of 1.15kg is of questionable value in the professional recommendation of one diet over another.
Competing interests: I wrote the article