An interesting scientific paper on the efficacy of different dietary approaches in type 2 diabetes recently caught my eye. The study has not received much media coverage although it certainly addresses a question of importance to millions of people worldwide.
More than 20 million people in the US have type 2 diabetes. According to the International Diabetes Foundation (IDF), the number of people diagnosed with diabetes in the last twenty years has risen from 30 million to over 246 million, or about 7.3% of the world population. Approximately 90% of those have type 2 diabetes. Diet and nutrition play a central role in the well-being of all those people.
The study, which is a systematic review, was published in a recent issue of the American Journal of Clinical Nutrition. A systematic review is an unbiased survey of all the scientific evidence available on a given question. In this case, Ajala and coworkers from Plymouth UK addressed the efficacy of different diets to induce weight loss and improve glycemic control and lipid profile among people with type 2 diabetes.
Type 2 Diabetes and Prediabetes
Before we go further, let me touch on few basic issues, just for the sake of clarification. Type 2 diabetes is a chronic condition that affects the way our body metabolizes sugar (glucose). Glucose is the body’s primary source of fuel. With type 2 diabetes, the body either resists the effects of insulin — a hormone that regulates the movement of sugar into our cells — or doesn’t produce enough insulin to maintain a normal glucose level.
Glucose comes from two major sources, food and the liver. Our liver produces and stores glucose. When glucose enters the blood stream, insulin is released from the pancreas. Insulin enables sugar to enter the cells of the body where it is used for energy production. Without insulin, or when insulin resistance is present, glucose builds up in the blood stream. This is what happens in diabetes. Elevated levels of blood glucose may cause a number of symptoms, and increase the risk of developing heart disease and stroke.
It is not fully understood why people develop type 2 diabetes, but certain factors increase the risk. Overweight is a risk factor. However, many overweight and obese individuals never have diabetes, and many people with type 2 diabetes are not overweight or obese. If our body stores fat primarily in the abdomen, the risk of diabetes is higher than if the body stores fat elsewhere such as on our hips and thighs. Family history and physical inactivity also increase the risk of diabetes.
The risk of type 2 diabetes increases with age. Lately, type 2 diabetes has become increasingly common in children, adolescents, and young adults. The main goals of therapy are to improve glucose metabolism and thereby reduce blood sugar levels and to mitigate the risk factors for the main complications of diabetes, heart disease, and stroke. Overweight often contributes significantly to the development of type 2 diabetes. Therefore weight loss often plays a large role in the treatment of the disorder.
Prediabetes is a condition in which blood sugar level is higher than normal, but not high enough to be classified as diabetes. Left untreated, prediabetes often progresses to type 2 diabetes. There is good evidence showing that dietary modification can prevent the progression from prediabetes to type 2 diabetes. Howvever, the optimal dietary approach to type 2 diabetes is less clear. Before I discuss the recent study by Ajala and coworkers, let’s have a look at the background stage.
What Is the Best Diet for Type 2 Diabetes?
For some years, experts and scientists have debated what dietary approach is best to control and treat type 2 diabetes. Most regulatory authorities, like the British Diabetic Association, European Association for the Study of Diabetes (EASD), American Diabetes Association (ADA), Canadian Diabetes Association and many more usually recommend a carbohydrate intake of 50-60% of total energy intake, total fat intake less than 30% of energy, with restriction of saturated and trans fat intake. Some experts believe there is insufficient evidence to justify these recommendations.
Almost five years ago, an international group of scientists and experts on diabetes, nutrition and carbohydrate metabolism published an overview paper suggesting a critical appraisal of the role of carbohydrate restriction in type 2 diabetes mellitus and the metabolic syndrome. The authors pointed out that current nutritional approaches often emphasized a reduction in dietary fat.
They believed that such approaches often were ineffective, leading to more reliance on drug therapy. They argued that carbohydrate restricted diets were at least as effective for weight-loss as low-fat diets and that the substitution of fat for carbohydrate was beneficial for the risk of cardiovascular disease. Furthermore, they provided evidence suggesting that carbohydrate restriction improved control of blood glucose and reduced insulin fluctuations. They believed the recommendation to reduce the intake of saturated fat in type 2 diabetes lacked scientific evidence.
The authors concluded: “Finally, while no systematic study of clinical practice has been done, anecdotal evidence suggests that carbohydrate restriction is a common clinical recommendation for diabetes. We believe that there is a need to codify these recommendations in light of current evidence.”
In the recent systematic review by Ajala and coworkers, data was collected from all studies published up to July 2011 that compared low carbohydrate, vegetarian, vegan, low glycemic index (GI), high fiber, Mediterranean, and high protein diets with control diets including low-fat, high-GI, ADA diet, EASD diet, and low-protein diets. Only randomized controlled trials with an intervention lasting longer than six months were selected. A total of 20 studies including 3073 individuals fulfilled the defined criteria and were selected for the metaanalysis. Measured outcomes were HbA1c (which reflects glucose control), difference in weight loss, and changes in HDL-cholesterol (“good cholesterol”), LDL-cholesterol (“bad cholesterol”) and triglycerides.
The low carbohydrate, low-GI, Mediterranean, and high protein diets all led to a greater improvement in blood glucose control (HbA1c) compared with their respective control diets, with the largest effect seen with the Mediterranean diet. Low-carbohydrate and Mediterranean diets led to a greater weight loss compared with their control diets. Low carbohydrate, low-GI, and Mediterranean diets all led to an elevation of HDL-cholesterol. Only the Mediterranean diet led to a significant reduction in triglycerides. High protein diets had no effects on markers of lipid profile. One study from their review compared the effects of a vegan diet to the low-fat ADA diet. The vegan arm had a significantly lower levels of total cholesterol, LDL-cholesterol, and HbA1c, indicating better glycemic control by the vegan diet. Similar results were obtained in one study that compared the effect of a vegan diet with the EASD diet, with more weight loss on the vegan diet.
Ajala and coworkers conclude that their review provides evidence that modifying the amount of macronutrients can improve glycemic control, weight, and lipids in type 2 diabetes. In their analysis, low carbohydrate diets appeared to provide superior weight loss, better control of blood glucose, and better lipid profile, compared with low-fat diets. The authors also conclude that vegan and vegetarian diet may improve glucose control and promote weight loss in type 2 diabetes.
The Mediterranean diet is rich in olive oil, legumes, unrefined cereals, fruit, and vegetables, low in meat and meat products, and with moderate contents of dairy products (mostly cheese and yogurt), fish and wine. The total fat in this diet is typically 25-35% of calories, with saturated fat less than 8% of calories. The meta-analysis indicates that a Mediterranean diet provides better control of blood glucose, greater weight loss, and a more favorable lipid profile compared with a conventional diet and ADA diet.
A meta-analysis of such widely different studies may be problematic. For example, the control diets differed significantly between studies and the duration of the studies ranged between six months and four years. The definition of a low carbohydrate diet varies between studies. While the authors acknowledge the limitations of their study, they believe that low carbohydrate, low-GI, Mediterranean and high-protein diets should be considered in the overall strategy of diabetes management.
What is the best diet for type 2 diabetes? Although there is probably not a simple answer, the question reflects one of the main challenges of modern medicine. It is likely that our dietary recommendations will have to be tailored to the needs of the individual. A one-size-fits-all approach is unrealistic. Although not providing any definitive answers, the study by Ajala and coworkers is an important contribution to our understanding of this highly important issue.
8 thoughts on “What Is the Best Diet for Type 2 Diabetes?”
“It is likely that our dietary recommendations will have to be tailored to the needs of the individual.” Swedes have done this already. In the Swedish dietary recommendation for diabetes (2011),low GI, moderately low carb, Mediterranean diet and “traditional diabetes diet” are all included as possible and viable options. I think this is the way to go.
The long term addherence to any version of healthy diets is the key. People have different food aversion, different preferences, activity levels, so forth, and thus may prefer one of these dietary patterns more easy and attractive to follow in the long run. However, I think low carb pattern should avoid large amounts of red and processed meat, butter and cream and favour fish, seafood, dairy and beans as protein sources.
“What is the best diet for type 2 diabetes? Although, there is probably not a simple answer, the question reflects one of the main challenges of modern medicine”
I think the solution is simple: my perspective comes from the global epidemiology and atherosclerosis research. I will provide a direct quote from the chief inspector of Framingham study, William Castelli:
“You know, we know that if I can get your total cholesterol down around let’s say 100 to 130 or so, and I have maybe not quite a billion people on the earth like that, and those people cannot get atherosclerosis. You know in the China Study, for example, when Chou En-lai was dying of cancer he started a study in China just like the Framingham Study. The only difference was it was in 880,000,000 people so it was a little larger than the Framingham Study. But you know they found these villages in China where you couldn’t get a heart attack or you couldn’t get diabetes and the women couldn’t get breast cancer and you know their total cholesterol were 127, but the chances we could ever get Americans down that low with diet and exercise are not good”
For diabetic person exercise and plant-based diet rich in complex carbohydrates is the key.
I am a big fan of your blog Axel, however I think you ought to use more of your background in cardiology as a platform for perspective. Diabetes is essentially a form of vascular disease, a heart healthy diet works for diabetes as well. I think you often tend to make things more complicated than they actually are.
“I have great respect for such people who explore “the baroque beauty of biology” in its infinite perplexities. But I must admit to greater admiration for the distinguished clinician or scientist who sees the whole picture, not just its complex parts, and who realizes the importance of simple ideas and even of “simple research” on those ideas. For example, the terrible biologic complexity of metaplasia and carcinoma in the bronchi would, of course, largely disappear with one simple (?) public health measure – cessation of cigarette smoking”
Thanks for pointing us toward the Ajala review. I concur with your conclusions Axel, and not only because they conform to my own bias about diet. Many patients tell me that unlike prior diets they have tried, the Mediterranean Diet is easy to follow and delicious. I just wonder when, if ever, the AHA and all the other august bodies that have been preaching the low-fat gospel for years will retract their erroroneous advice and admit that they have done harm.
Thank you Axel for your summary of the meta study and your recommendation. I seem to be on the right track, considering I am in the risk zone for diabetes. /Martin
Thanks for your comment Martin, and thanks for reading my blog. From what I have seen on FB in the last year I assume you are under the influence of the Mediterranean diet/lifestyle. From a health perspective that is a good choice. My best regards to you and your family in Sweden.
Doc, you say ‘The Mediterranean diet is rich in olive oil, legumes, unrefined cereals, fruit and vegetables, low in meat and meat products, and with moderate contents of dairy products (mostly cheese and yogurt), fish and wine.’ I’ve never eaten, or seen, an unrefined cereal in Spain, Italy or Greece, so I don’t know whether the version of a Mediterranean diet used for the research used whole grains or whether this is a misunderstanding somewhere. Although there is white pasta (as a separate course) in Italy, there’s not much of it in Spanish or Greek food, but white rice and potatoes are eaten in those countries (and white rice in Italy too). None of those countries overload on carbs, though, in contrast to the prevalent American and UK junk-food diets. Meat (including air-dried ham and sausage) is regularly eaten in Mediterranean countries, as is cheese. Fish is often eaten and frequently fried. Oily fish doesn’t seem to be the favourite fish to eat, generally speaking. Mediterranean people in middle age, however, are inclined to put on weight. The French still have a better health profile that the Spanish and Italians.
Richard wrote: ‘Diabetes is essentially a form of vascular disease, a heart healthy diet works for diabetes as well.’ Is that the heart-healthy diet that calls for low fat and high carbohydrate? Because that’s the one that people have been following since the 1980s and getting fatter and more ill.
I think we have to bear in mind that with all these dietary suggestions the important point is to eat real food (as is true in the Mediterranean and French diets) and not manufactured foods such as polyunsaturated oils and margarines and not to fill ourselves up with large amounts of grains and sugars, which are not a natural way to eat. Meat, poultry, eggs and fish are good basic foods that should be eaten with vegetables and some fruits. Dairy is fine if you are not intolerant to it. Butter is good to eat – it’s natural. As the article above notes, ‘They argued that carbohydrate restricted diets were at least as effective for weight-loss as low-fat diets, and that the substitution of fat for carbohydrate was generally beneficial for the risk of cardiovascular disease. ‘
It’s time we put away the fear of fat and recognise that it is needed by the body. Perhaps it’s also time to stop seeing the French diet as a paradox and ask why the French remain one of the leanest people in Europe who have the lowest amounts of heart disease.
Jan C wrote:
“I don’t know whether the version of a Mediterranean diet used for the research used whole grains or whether this is a misunderstanding somewhere”.
The contemporary med diet has nothing to do with the sort of med diet that was being consumed by the poor peasants of Crete and Southern Italy in the 1950s. Keys observed already in 1950s that rich napolinians that were part of the Rotary club were not healthy and had high cholesterol levels. Rockefeller institute conducted a large epidemiological survey study on Crete during late 1940s. The diet was plant-based one, quite high in unrefined cereals, whole-grain pasta and wheat bread, etc. and low in animal products (which accounted for only 7% of calories). The diet consumed by poor Southern Italians was similar except much lower in fat (around 20% calories). Ikaros island in Greece which harbor one of the most healthiest and long-living people in Europe today is famous for its stone-ground wheat bread. Other dietary staples are legumes, potatoes and the olive oil.
“I think the solution is simple: my perspective comes from the global epidemiology and atherosclerosis research. I will provide a direct quote from the chief inspector of Framingham study, William Castelli:”
This question cannot be approached by anecdotes but by analysing the available research literature that meets the properly set inclusion criteria. As such, the current review points out that a multitude of approaches work.
More focus on the essentials, less copy/pasting.