Updated: Nov 20
Welcome to our long read on type 2 diabetes and diet. Both type 2 diabetes, and its precursor pre-diabetes, are dramatically on the rise. There is a great deal of debate on the subject of suitable diets and eating practices for type 2 diabetes, in particular how best to manage blood sugar and to achieve weight loss. Food is an emotional subject, science is complex and conflicting viewpoints on ketogenic, plant based, even carnivore diets, only add to the confusion.
The purpose of this article is to shine a light on what the science says about diet and diabetes. We will review the official dietary guidelines made by key national level bodies AND we will review the scientific literature that informs their decisions. We hope that by bringing the research to light we can have an informed conversation around the subject.
As ever, please talk to your doctor or medical practitioner most familiar with your medical history before implementing any changes in diet, exercise or lifestyle, especially if you are under treatment. Links to any supporting studies or resources are at the end of page.
We will quote extensively from scientific papers that are meta-analyses and systemic reviews. These are studies that combine the results of multiple scientific papers to highlight trends in any given subject, to demonstrate the preponderance of the evidence. They are not, however, completely free from inherent biases or issues with the data. It is possible that the results from some meta-analyses differ from others due to their selection of specific studies and interpretation of data. We have also generally avoided quoting from single studies except where directly relevant.
Government and National Recommendations on Diet
On a national level government agencies set dietary guidelines. Let us set the scene with the dietary recommendations from the USA and its Department of Agriculture (USDA) – the authority that creates the government recommendations:
“The 2020 Dietary Guidelines Advisory Committee reviewed newly published evidence using a systematic evidence scan and determined that the conclusion drawn by the 2015 Dietary Guidelines Advisory Committee generally reflects the current state of science:
Moderate evidence indicates that healthy dietary patterns higher in vegetables, fruits, and whole grains and lower in red and processed meats, high-fat dairy products, refined grains, and sweets/sugar-sweetened beverages reduce the risk of developing type 2 diabetes.” Boushey C, Ard J, Bazzano L, Heymsfield S, Mayer-Davis E, Sabaté J, Snetselaar L, Van Horn L, Schneeman B, English LK, Bates M, Callahan E, Butera G, Terry N, Obbagy J. Dietary Patterns and Risk of Type 2 Diabetes: A Systematic Review [Internet]. Alexandria (VA): USDA Nutrition Evidence Systematic Review; 2020 Jul. PMID: 35263067.
This dietary advice is broadly in keeping with the official guidelines of other nations’ medical authorities, from Singapore to the UK. But can we trust the advice of government bodies? Is their thinking biased, potentially compromised by commercial interests? Or, due to lengthy bureaucratic processes, are their statements out of date when compared to the latest published findings?
What do national organisations that are involved type 2 diabetes say?
American Diabetes Association
The 2019 Nutrition Consensus report from the American Diabetes Association states that the report is “intended to provide clinical professionals with evidence-based guidance about individualizing nutrition therapy for adults with diabetes or prediabetes.” so that seems like a good place to start. Given the amount of debate around diet and diabetes one of the first statements is not unsurprising:
"Though it might simplify messaging, a “one-size-fits-all” eating plan is not evident for the prevention or management of diabetes, and it is an unrealistic expectation given the broad spectrum of people affected by diabetes and prediabetes, their cultural backgrounds, personal preferences, co-occurring conditions (often referred to as comorbidities), and socioeconomic settings in which they live.” Alison B. Evert, Michelle Dennison, Christopher D. Gardner, W. Timothy Garvey, Ka Hei Karen Lau, Janice MacLeod, Joanna Mitri, Raquel F. Pereira, Kelly Rawlings, Shamera Robinson, Laura Saslow, Sacha Uelmen, Patricia B. Urbanski, William S. Yancy; Nutriti https://doi.org/10.2337/dci19-0014
Here are their primary recommendations on suitable eating practices:
“MACRONUTRIENTS, Consensus recommendations
Evidence suggests that there is not an ideal percentage of calories from carbohydrate, protein, and fat for all people with or at risk for diabetes; therefore, macronutrient distribution should be based on individualized assessment of current eating patterns, preferences, and metabolic goals.
When counseling people with diabetes, a key strategy to achieve glycemic targets should include an assessment of current dietary intake followed by individualized guidance on self-monitoring carbohydrate intake to optimize meal timing and food choices and to guide medication and physical activity recommendations.
People with diabetes and those at risk for diabetes are encouraged to consume at least the amount of dietary fiber recommended for the general public; increasing fiber intake, preferably through food (vegetables, pulses [beans, peas, and lentils], fruits, and whole intact grains) or through dietary supplement, may help in modestly lowering A1C.”
While the report goes on to review the pros and cons of multiple eating practices, the only clear and definitive announcement of what should be eaten is ‘eat more fibre’. The other recommendations are vague to say the least. Given the multitude of divergent statements to be found online no wonder that people are confused and that the online space can be so argumentative.
Dietary Advice from Singapore
Specific dietary advice comes in various forms. Key recommendations from Diabetes Singapore are as follows. Please note that there is more detail within the website, we have quoted the primary recommendations only.
"1. Make sure your diet is balanced
2. Consume sugar in moderation
3. Rice and other starches should be in moderation
4. Dietary fruits that are good for diabetics
5. Limit your fat intake
6. Consume alcohol in moderation
7. Follow My Healthy Plate"
The Balance of Foods in the Diet
Similar to the advice that one might receive from a visit to the doctor’s office, most recommendations state ‘eat more of this’ and ‘eat less of that’. The following study on the risks of food groups provides the detail behind the recommendations:
"The results of the present meta-analysis add further scientific evidence supporting the inclusion of some food groups into food-based dietary guidelines for their potential role in preventing T2D. Optimal consumption of whole grains, vegetables, fruits, and dairy, and non-consumption of red meat, processed meat, sugar sweetened beverages, and eggs was associated with an 81% reduced risk of T2D. Previous studies could show that diet plays an important role in T2D risk…
One of the important findings of our study is that reducing the consumption of risk-increasing foods seems to have more impact on occurrence of T2D than favoring foods that reduce risk by increasing consumption. The impact on T2D risk was larger for non-consumption of red and processed meats, SSB (sugar sweetened beverages), and eggs (threefold risk increase) compared to the consumption of whole grains, dairy, fruits, and vegetables (42% risk reduction).” Schwingshackl, L., Hoffmann, G., Lampousi, AM. et al. Food groups and risk of type 2 diabetes mellitus: a systematic review and meta-analysis of prospective studies. Eur J Epidemiol 32, 363–375 (2017). https://doi.org/10.1007/s10654-017-0246-y
One particular statement caught our attention “One of the important findings of our study is that reducing the consumption of risk-increasing foods seems to have more impact on occurrence of T2D than favoring foods that reduce risk by increasing consumption.”
You have to be strict with the bad stuff if you want to be healthy.
Fibre, The Missing Nutrient?
Fibre, the only essential dietary macronutrient that the American Diabetes Association consensus report highlights, is important. What is the recommended amount and by how much can it help?
“The findings from our systematic review and meta-analyses have demonstrated the likely benefits of increasing dietary fibre in people with diabetes. Prospective cohort study data indicate a reduced risk of total mortality in adults with diabetes. Given that in many relatively affluent societies most adults consume around 20 g of dietary fibre per day, our data suggest that a 15 g increase to 35 g per day might be a reasonable target that would be expected to reduce risk of premature mortality by 10% to 48%.” Reynolds AN, Akerman AP, Mann J. Dietary fibre and whole grains in diabetes management: Systematic review and meta-analyses. PLoS Med. 2020 Mar 6;17(3):e1003053. doi: 10.1371/journal.pmed.1003053. PMID: 32142510; PMCID: PMC7059907.
As fibre is a key part of a healthy diet, let’s see the specifics from several key territories:
USA, we will quote from Harvard’s health website as the USDA fibre recommendations are based on daily caloric consumption which makes for a complicated calculation “American adults eat 10 to 15 grams of total fiber per day, while the USDA's recommended daily amount for adults up to age 50 is 25 grams for women and 38 grams for men.”
Singapore, SingHealth “An average Singaporean consumes 13 grams of dietary fibre per day. The recommended amount is 30 grams per day.”
United Kingdom, National Health Service: “Government guidelines say our dietary fibre intake should increase to 30g a day, as part of a healthy balanced diet. As most adults are only eating an average of about 20g day, we need to find ways of increasing our intake.”
The same meta-analysis as above (Reynolds, Ackerman, Mann) provides further details on whole grains, a food type sometimes vilified in online debates.
"Whole grain products have high concentration of fibers, which delay gastric emptying, therefore slowing glucose release in circulation. This results in reduced postprandial insulin response and could improve insulin sensitivity The aforementioned associations are also supported by the observed protective effect of healthy dietary pattern against developing T2DM.
There seems to be a strong case for eating fibre and, for most of us, this means eating a lot more fibre. Perhaps surprising to some, this recommendation is to eat foods considered to be high in carbohydrates. But note, and this is vitally important, these are minimally processed carbohydrates - typically what are known as whole foods. This is the opposite of processed and ultra-processed carbohydrates (sugars and flours) that those with type 2 diabetes have been told to limit or avoid.
The Role of Meat
Numerous studies have highlighted a negative relationship between meat and diabetes. On a global basis results seem to differ between different regions and populations as to how great a role meat has to play. Could this be due to differences in the design of the selected studies or the populations being studied and their own, unique lifestyle factors? It is hard to say. In broad strokes the the research indicates:
“When comparing the highest with the lowest category of meat intake, the summary relative risk of T2D was 1.33 for total meat, 1.22 for red meat, 1.25 for processed meat, 1.00 for poultry and 1.01 for fish.
In the dose-response analysis, each additional 100g/day of total and red meat, and 50g/day of processed meat, were found to be associated with a 36%, 31% and 46% increased risk of T2D, respectively. In addition, there was evidence of a non-linear dose-response association between processed meat and T2D, with the risk increasing by 30% with increasing intakes up to 30g/day.” Yang X, Li Y, Wang C, Mao Z, Zhou W, Zhang L, Fan M, Cui S, Li L. Meat and fish intake and type 2 diabetes: Dose-response meta-analysis of prospective cohort studies. Diabetes Metab. 2020 Oct;46(5):345-352. doi: 10.1016/j.diabet.2020.03.004. Epub 2020 Apr
How exactly does meat increase the risk of diabetes?
“Similarly, other meta-analyses indicated that the positive association between a diet high in red or processed meats and diabetes risk remained after adjusting for the intake of saturated and total fat as well as BMI. It was assumed that nitrosamine and advanced glycation end-products in processed meats might further contribute to the development of diabetes. Moreover, meat supplies substantial amounts of heme iron, which accelerates oxidative stress, consequently affecting insulin resistance and glucose metabolism.” Lee Y, Park K. Adherence to a Vegetarian Diet and Diabetes Risk: A Systematic Review and Meta-Analysis of Observational Studies. Nutrients. 2017 Jun 14;9(6):603. doi: 10.3390/nu9060603. PMID: 28613258; PMCID: PMC5490582.
Likely its effect relates to a combination of factors: high levels of heme iron, meat’s negative affect on the gut microbiome, that high heat cooking techniques (grilling, frying and roasting) create harmful advanced glycation end products. Sorry to say that the much beloved Maillard reaction (browning) of meat is not healthy. Daily meat intake, in affluent countries, is also associated with weight-gain. A significant number of people with diabetes are not overweight, they are normal weight and have passed their personal fat threshold.
Another factor to consider, applicable to all discussions relating to diet, is that when one eats one thing it is at the expense of another. Perhaps eating more meat equates to fewer health promoting vegetables or whole grains. One has to look at the totality of the diet as nothing is eaten in isolation. And, in turn, health is affected by other lifestyle factors, not purely diet.
Popular Eating Practices for Type 2 Diabetes
So, now that we have reviewed specifics relating to individual macronutrients and food types, how does this apply to our own kitchen or dining table? What eating patterns are high in fibre and complex carbohydrates? What eating patterns are low in red or processed meat? Do any studies provide examples that have been shown to have beneficial health affects relating to diabetes? The answer, happily, is Yes.
The Mediterranean Diet
Perhaps the best studied is the traditional Mediterranean eating pattern as highlighted in the so called Blue Zones, hotspots around the world of great longevity. Similar to many traditional diets around the world it is rich in whole (unprocessed) foods and relatively low in meat.
“Current evidence indicates that the Mediterranean diet is effective in improving both glycaemic control and cardiovascular risk factors in people with type 2 diabetes, and should therefore be considered in the overall strategy for management of people with diabetes. The convergence analysis of prospective studies and interventional trials was satisfied: the Mediterranean diet is able to reduce the incidence of future diabetes by 19–23%.
A significant reduction of type 2 diabetes has been found to be associated with greater consumption of healthy dietary patterns, including the Mediterranean diet, the DASH (Dietary Approach to Stop Hypertension) diet, the AHEI (Alternative Healthy Eating Index) and various a posteriori defined prudent/healthy dietary patterns, derived by factor or cluster analysis. All the protective dietary patterns, including the vegetarian diet, present many similarities with the Mediterranean diet, since they are mostly plant-based and include a high consumption of whole-grain foods, fruit and vegetables.” Esposito K, Maiorino MI, Bellastella G, et al A journey into a Mediterranean diet and type 2 diabetes: a systematic review with meta-analyses BMJ Open 2015;5:e008222. doi: 10.1136/bmjopen-2015-008222
Another advantage of this eating pattern is likely due to the high level of inflammation reducing polyphenols (antioxidants):
“Polyphenols are highly prevalent in plant-based diets, such as the Mediterranean Diet (MedDiet), and especially abundant in fruits, vegetables, legumes, cocoa, coffee, and red wine. In addition, extra-virgin olive oil and nuts, both key components of the MedDiet, are also polyphenol-rich foods.
Given the abundant evidence from human studies regarding the intake of polyphenols, and their food sources, on related-diabetes risk factors, this narrative review has focused on well-conducted clinical trials and prospective cohort studies with special attention paid to extra-virgin olive oil, nut, and red wine consumption but also other polyphenol-rich foods. These key components of the MedDiet were inversely associated with insulin resistance and T2D risk in observational studies. The intake of specific polyphenols, especially flavan-3-ols and their food sources, has demonstrated overall beneficial effects on improving insulin resistance, chronic systemic inflammation, oxidative stress, and other cardiometabolic risk factors in trials that tested effects of acute, moderate-term, or relatively long-term (up to a year) intake of flavan-3-ols. Moreover, findings from prospective cohort studies have suggested inverse associations between the intake of total flavonoids and specific flavonoid subclasses and the risk of T2D, although some controversial results still exist.” Guasch-Ferré M, Merino J, Sun Q, Fitó M, Salas-Salvadó J. Dietary Polyphenols, Mediterranean Diet, Prediabetes, and Type 2 Diabetes: A Narrative Review of the Evidence. Oxid Med Cell Longev. 2017;2017:6723931. doi: 10.1155/2017/6723931. Epub 2017 Aug 13. PMID: 28883903; PMCID: PMC5572601.
Plant Based or Plant Forward Diets
What about other diets high in fibre, say, vegetarian or plant forward diets? These too have been studied for their role in diabetes.
“Cumulative evidence has emphasized that a vegetarian diet has beneficial effects on diabetes prevention, partly due to the lower body mass index (BMI) of vegetarians when compared to their omnivorous counterparts. However, the observed inverse association between a vegetarian diet and the risk of diabetes remained statistically significant after adjusting for BMI…
Vegans in particular often had the lowest odds of diabetes when compared to other types of vegetarians; they also had lower levels of intramyocellular lipids, which may be related to insulin resistance. Similarly, a meta-analysis of results from intervention studies showed that a vegetarian diet significantly improved HbA1c level in patients with diabetes.
Several meta-analyses suggested that whole grains, fruits, and vegetables (in particular, root vegetables and leafy greens, which are high in dietary fibers, beta-carotene, vitamin C, and magnesium) had beneficial effects on diabetes prevention. The most recent meta-analysis of prospective studies using a dose-response analysis revealed that the risk of type 2 diabetes mellitus was reduced by up to 81% by optimally consuming risk-reducing foods such as whole grains, vegetables, fruits, and dairy while simultaneously avoiding risk-increasing foods such as red and processed meats, sugar-sweetened beverages, and eggs. Furthermore, no consumption of risk-increasing foods had more protective effects on developing diabetes than the consumption of risk-reducing foods.” Lee Y, Park K. Adherence to a Vegetarian Diet and Diabetes Risk: A Systematic Review and Meta-Analysis of Observational Studies. Nutrients. 2017 Jun 14;9(6):603. doi: 10.3390/nu9060603. PMID: 28613258; PMCID: PMC5490582.
The Ketogenic Diet
The consensus report from the American Diabetes Association summarises the results of the ketogenic diet as follows:
“Low-carbohydrate eating patterns, especially very low-carbohydrate (VLC) eating patterns, have been shown to reduce A1C and the need for antihyperglycemic medications. These eating patterns are among the most studied eating patterns for type 2 diabetes. One meta-analysis of RCTs that compared low-carbohydrate eating patterns (defined as ≤45% of calories from carbohydrate) to high-carbohydrate eating patterns (defined as >45% of calories from carbohydrate) found that A1C benefits were more pronounced in the VLC interventions (where <26% of calories came from carbohydrate) at 3 and 6 months but not at 12 and 24 months.
Another meta-analysis of RCTs compared a low-carbohydrate eating pattern (defined as <40% of calories from carbohydrate) to a low-fat eating pattern (defined as <30% of calories from fat). In trials up to 6 months long, the low-carbohydrate eating pattern improved A1C more, and in trials of varying lengths, lowered triglycerides, raised HDL-C, lowered blood pressure, and resulted in greater reductions in diabetes medication. Finally, in another meta-analysis comparing low-carbohydrate to high-carbohydrate eating patterns, the larger the carbohydrate restriction, the greater the reduction in A1C, though A1C was similar at durations of 1 year and longer for both eating patterns.”
The ketogenic diet is very effective at managing blood sugar levels, zero carbohydrate in = zero sugar to manage. However, after a year or more the results seem to be comparable to other diets.
What about addressing the important issue of weight, how does the ketogenic diet compare for weight-loss against other diets?
“Low‐carbohydrate diets or balanced‐carbohydrate diets: which works better for weight loss and heart disease risks? Key messages:
There is probably little to no difference in the weight lost by people following low‐carbohydrate weight‐reducing diets (also known as 'low‐carb diets') compared to the weight lost by people following balanced‐carbohydrate weight‐reducing diets, for up to two years.
Similarly, there is probably little to no difference between the diets for changes in heart disease risks, like diastolic blood pressure, glycosylated haemoglobin (HbA1c, a measure of blood sugar levels over 2‐3 months) and LDL cholesterol (‘unhealthy’ cholesterol) up to two years.
This was the case in people with and without type 2 diabetes."
Naude CE, Brand A, Schoonees A, Nguyen KA, Chaplin M, Volmink J. Low-carbohydrate versus balanced-carbohydrate diets for reducing weight and cardiovascular risk. Cochrane Database Syst Rev. 2022 Jan 28;1(1):CD013334. doi: 10.1002/14651858.CD013334.pub2.
We found a specific study that compared the ketogenic diet to a Mediterranean diet, the KETO-MED study. This was a randomised, crossover, interventional trial. In scientific terms this a high quality study as the participants were consecutively placed on each of the two diets, effectively using themselves as the control. 40 participants with prediabetes or type 2 diabetes followed both a well-formulated ketogenic diet (WKFD) and the Mediterranean for 12 weeks each, in random order. Why ‘well-formulated’? To ensure that the diet was sufficiently high in fat to induce ketosis, not high in meat as many people interpret and enjoy the diet when it comes to their own plates.
“HbA1c values were not different between diet phases after 12 weeks, but improved from baseline on both diets, likely due to several shared dietary aspects. The WFKD led to a greater decrease in triglycerides, but also had potential untoward risks from elevated LDL cholesterol and lower nutrient intakes from avoiding legumes, fruits, and whole, intact grains, as well as being less sustainable.” Christopher D Gardner and others, Effect of a ketogenic diet versus Mediterranean diet on glycated hemoglobin in individuals with prediabetes and type 2 diabetes mellitus: The interventional Keto-Med randomized crossover trial, The American Journal of Cli https://doi.org/10.1093/ajcn/nqac154
So, similar results for blood sugar from both diets but issues with compliance for the keto diet as it was found to be unpalatable for the participants. In the long-term, the high cholesterol levels from a ketogenic diet are a cause for concern. Unlike for other better studied eating patterns there are, as of yet, few long-term studies to understand the ketogenic diet’s health outcomes. We simply don’t know.
“Further trials are needed to clarify the balance between the benefits and harms of this dietary approach, including more thorough reporting of potential detrimental effects (such as those on renal function) and a wider assessment of psychological well-being and quality of life. The exploration of further outcomes, such as cognitive decline and the design of larger scale trials on hard endpoints, such as major cardiovascular events, the incidence of diabetes and renal failure, would provide a more robust assessment of the clinical effects of specific carbohydrate restriction in the treatment of obesity.” Silverii, GA, Cosentino, C, Santagiuliana, F, et al. Effectiveness of low-carbohydrate diets for long-term weight loss in obese individuals: A meta-analysis of randomized controlled trials. Diabetes Obes Metab. 2022; 24( 8): 1458- 1468. doi:10.1111/dom.14
Type 2 diabetes and its relation to eating practices, people, their lives, is complicated. There is no single 'right' nor 'wrong' diet or - we prefer - eating practice. Why the emphasis on eating practice? Because once a weight loss or health goal is achieved, with diabetes in remission or reversed, the individual has to be able to continue healthy eating in the long-term. There cannot be a reversion to the previous eating pattern that was a cause of the diabetes.
When it comes to the plate, the consensus of all bodies is that fibre consumption needs to be increased, to meet the daily recommended intakes. To consume more whole grains, greens, beans and fruit. This is a plant forward diet.
Recommendations consistently advise to reduce consumption of red and processed meat. What does this mean in daily living? Smaller portions, a focus on fish or poultry, increasing plant based sources of protein, and a change in cooking techniques. Some might consider incorporating more plant based meals into their days or plant based days into their weeks, or potentially following any number of plant forward diets.
In the last few years the ketogenic diet has become increasingly popular. Short-term weight-loss is rapid and for those that have struggled to lose weight this can be a powerful incentive to follow the diet. Very low carbohydrate intake successfully controls blood sugar levels whilst at the same time restricting some of the healthiest high fibre foods (whole grains, beans, legumes) associated with positive long-term health outcomes. In the long-term the diet does not have any weight-loss advantage over others. It is potentially harmful due to its effect on raising cholesterol and increasing the risk of heart disease. There are now, however, some promising studies on ketogenic diets focused on healthier, unsaturated fats.
Studies have also shown that time restricted feeding, eating during a limited daily time window, supports weight loss. This is likely as the strict timings makes dieting easier to follow, as opposed to counting calories per se.
An important concept in diabetes is that of the personal fat threshold. This has led to the development of specifically formulated, successful weight loss diets that have put type 2 diabetes into remission.
In this article we have focused on diet. Successfully managing, or indeed reversing, type 2 diabetes cannot be achieved purely through eating practices. Exercise, sleep, stress, work-life balance, social relationships - the pillars of health - have a role to play. This requires lifestyle change, where we at The Whole Health Practice dedicate our energy, to support our clients on their unique journeys to health.
National Diabetes Bodies
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