Diabetes affected 3.4 million (9.3%) of Canadians in 2015 while prediabetes (increased blood sugar levels not yet high enough to be called “diabetes”) affected 5.7 million (22%) of Canadians. It is expected that by 2025 the incidence of diabetes will increase by 44%. The impact of diabetes is enormous. It is the cause of a myriad of disabilities as well as early death and is a large burden on our healthcare system.
What is diabetes?
Diabetes is the chronic elevation of blood sugar levels. Type 1 diabetes results when the pancreas does not produce enough insulin. Type 2 diabetes occurs when the body becomes resistant to the effect of insulin. Insulin is the hormone produced by your pancreas which allows your body to use sugar for energy or store it for later use. The vast majority of diabetes today is type 2. When you eat carbohydrates, the body breaks them down into simple sugars such as glucose, the desired fuel for powering the cells of the body. Glucose is turned into energy through a biochemical process called the Krebs cycle. Because our brains are not capable of surviving for very long without an energy source, our bodies have a back-up plan. If sugar is not available, fat can also be used as an energy source. When blood sugar is constantly high, damage to blood vessels occurs that will develop into the many consequences of diabetes including kidney disease and failure, blindness, heart attacks, strokes, nerve damage (numbness, tingling and pain) and poor circulation and lack of feeling in the legs and feet that can lead to amputations.
Where does fat fit into diabetes?
In 2004 the American Diabetes Association stated,
“…there is little evidence that total carbohydrate is associated with the development of type 2 diabetes. Rather, a stronger association has been observed between total fat and saturated fat and type 2 diabetes.”(25)
Excess body fat is the number one risk factor for diabetes and it is the fat that builds up inside muscle cells and other organs that causes insulin resistance. (Insulin resistance means that the cells are not responding to the insulin that the body produces.) Obviously this troublesome fat can come from the food you eat but, perhaps surprisingly, body fat stores are another source. Human beings are born with a certain number of fat cells. More fat cells can be created during puberty. However, during the remainder of life, very few new fat cells are produced. Fat cells can continue to accumulate fat until they are so bloated that fat begins to leak back out of them. In other words, a person’s own fat can spill out of cells into the blood stream, adding to the fat burden in the blood and ending up clogging cells and preventing insulin from doing its work. Insulin is the “key” that allows glucose to enter the cells; fat inside cells blocks that pathway (2,3,4,5,6). If sugar cannot enter cells, the cells cannot get the energy they need to perform their important functions in the body.
For those interested in details, here is a quick rundown of what actually happens in the body during prediabetes that ends up in insulin resistance. Our muscles are our biggest consumers of sugar so insulin must work efficiently in the muscles to ensure they get their fuel. Fat in the blood stream (fatty acids) triggers production of free radicals and, after the fat is lodged into muscles cells, toxic breakdown products also begin to be produced. This is especially true of saturated fats because they are exceedingly efficient at producing the free radicals and inflammation that can impair insulin performance (26). Inflammation blocks insulin from opening up the “glucose gate”, the mechanism that allows blood sugar to enter cells. No matter how much insulin is produced, the fat-compromised cells cannot utilize it and so the sugar level in the blood continues to rise. During the early stages of this process, the pancreas pumps out more and more insulin to try to overcome the fat-induced insulin resistance. The now abnormally high insulin level causes even more fat to enter the muscle cells and fat also begins to build up in the liver, soon rendering the liver insulin resistant. Normally the liver is in constant production of the blood sugar that is needed to keep our brain alive between meals. After eating a meal, it is the insulin that turns off the liver glucose production until it is needed again. However, a fatty insulin-resistant liver will not respond to these “normal” signals and continues to pump out more blood sugar. The pancreas in turn tries hard to correct the problem and continues to pump out more insulin, encouraging additional fat to accumulate in the liver. This is the first vicious cycle –fatty muscle cells lead to an increasingly fatty liver. In an attempt to repair itself, the fatty liver begins to dump its excess fat back into the bloodstream in the form of VLDL (Very Low Density Lipoprotein). This fat in turn builds up inside the cells of the pancreas. Fatty muscles lead to a fatty liver which leads to a fatty pancreas. Excess fat in the pancreas is toxic to the insulin-producing beta cells in the pancreas and they begin to die. Inevitably insulin production starts to fall. Sugar levels go up and stay up and we have type 2 diabetes. (2,3,4,5,6)
What does science tell us?
Hundreds of studies have been completed looking into the prevention of diabetes. Dr. Neal Barnard, one of the first researchers to perform a randomized trial looking into diet and diabetes, placed 100 overweight, diabetic people on either a vegan diet (unlimited in calorie intake) or a reduced-calorie, low fat ADA (American Diabetes Association) diet. Both groups received counselling over the 74 week length of the trial and measurements were taken of body weight, A1C (a measure of blood sugar level over a three month period) and LDL cholesterol. The results were surprising. The vegans, who ate many more carbohydrates, showed significantly better blood sugar control, lower cholesterol and lost more weight than those following the ADA diet (11,12).
In 2016, the Harvard T.H. Chan School of Public Health completed a twenty year study following 200,000 health professionals. They found that eating a healthy plant-rich diet low in animal foods is associated with an average 20% reduced risk of type-2 diabetes. Those on the most healthy diet, centered around whole grains, fruits, vegetables, legumes and nuts, with minimal animal-sourced foods enjoyed a 34% reduced risk of type-2 diabetes while those eating more refined and processed foods, more animal-sourced foods and sugary drinks had a 16% increased risk of type-2 diabetes. Furthermore, a modest reduction in animal-based foods (from 5 or 6 daily servings down to 4 servings a day) was in itself associated with a lower risk of type-2 diabetes (9).
The very powerful EPIC (European Prospective Investigation into Cancer and Nutrition) tells a similar story. This huge work involved hundreds of top scientists following 521,000 people recruited from ten European countries for twelve years. The conclusions?
Meat, especially processed meat, is significantly associated with the development of type-2 diabetes.
Fruit and vegetable consumption is associated with a decrease in type-2 diabetes development.
Glucose and fructose consumption is correlated with reduced risk of type-2 diabetes. Indeed replacing only 5% of the saturated fats in the diet with fructose from fruit reduces risk of developing diabetes by whopping 30% (10).
The large population of Seventh Day Adventists in Loma Linda, California provides an ideal group for nutrition studies. As a unit, they are much healthier than most of their fellow Americans – they do not drink or smoke, they exercise regularly and they consciously strive for good health. Many of them do not eat animals but some do and they offer a good mix of diets including meat eaters, fish eaters, vegetarians and vegans. Seventh Day Adventist studies show a significant association between animal protein and diabetes development. Though diabetes incidence is much lower in this population than in the rest of the US, the studies still show a graduated increase in the risk of diabetes as the amount of animal protein consumed is increased. Vegans have the lowest risk, at 2.9%. Vegetarians, who eat no meat but do eat dairy and eggs, come next at 3.2%. Pescatarians (who add fish to the regular vegetarian diet) have a 4.8% risk of diabetes. Meat eaters bring up the rear with a 7.6% diabetes risk (13,14,15,16). A 2013 update study, the Adventist Health Study-2, reiterated these results. This time 89,000 people were followed for fifty years and, once again, eating meat was found to correlate with significantly higher rates of diabetes (7).
The updated conclusion reveals that, COMPARED TO PEOPLE WHO EAT MEAT EVERY DAY;
Flexitarians (those who eat meat only about once a week) have about 3/4 the diabetes risk
Pescatarians (those who eat fish but no other meat) have about 1/2 the diabetes risk
Vegetarians (those who eat no meat at all) have about 1/3 the diabetes risk
Vegans (those who eat only plants) have about 1/4 the diabetes risk
Next we can look at the Harvard University studies, the Nurses’ Health Study and the Health Professionals Follow-up Study. The First Nurses’ Study began in 1976 and followed 122,000 nurses. The Second Nurses’ Study started in 1989 and followed 116,000 nurses. The Health Professionals Follow-up Study started in 1986 and followed 51,000 male health care professionals. It should come as no surprise by now that significant associations emerged linking meat, including processed meat, with increases in diabetes development. To quantify this, increasing meat consumption by only half a serving a day increased the risk of developing diabetes by 48% (17,18,19,20,21).
A 2010 prospective study saw 43 people adopt a diet rich in fruits, vegetables, beans, seeds and nuts and no animal foods or junk foods. Participants were rewarded with substantial drops in blood sugar and insulin levels, lower levels of inflammation and lower blood lipids (22). Epidemiological studies also reveal diabetes protection from plant-based diets (23,24). A study completed at the Imperial College of London compared plant-eaters with omnivores of the same body weight and discovered that the plant-eating subjects had better insulin sensitivity, blood sugar and insulin levels along with significantly better pancreatic beta-cell function (8).
Need we go on? Study after study comes back with the same results. A diet higher in plants reduces the risk of diabetes. The question that comes to mind is what exactly is causing these dramatic health improvements. Is it the elimination of saturated fats or other fat types? Is it the reduction of inflammation? Could it be some attribute of plants themselves? Stay tuned for Part Two of “What Does Eating Plants Do For Type 2 Diabetes?” to learn more.
1 Virtanen, H.E., Koskinen, T.T., Voutilainen, S., et al. Intake of different dietary proteins and risk of type-2 diabetes in men: the Kuopio Ischaemic Heart Disease Risk Factor Study. British Journal of Nutrition. Mar 2017; 117(6): 882-893.
2 Taylor, R. Pathogenesis of type 2 diabetes: Tracing the reverse route from cure to cause. Diabetologia. 2008 Oct; 51(10): 1781-1789.
3 Taylor, R. Banting Memorial lecture 2012: Reversing the twin cycles of type 2 diabetes. Diabet Med. 2013 Mar; 30(3):267-75.
4 Lichtenstein, A.H., Schwab, U.S. Relationship of dietary fat to glucose metabolism. Atherosclerosis. 2000 Jun; 150(2):227-43.
5 Kraegen, E.W., Cooney,G.J. Free fatty acids and skeletal muscle insulin resistance. Curr Opin Lipidol. 2008 Jun; 19(3):235-41
6 Martins, A.R., Nachbar, R.T., Gorjao, R., Vinolo, M.A. et al. Mechanisms underlying skeletal muscle insulin resistance induced by fatty acids: important of mitochondrial function. Lipids Health Dis. 2012 Feb; 11:30.
7 Tonstad, S., Stewart, K., Oda, K. et al. Vegetarian diets and incidence of diabetes in the Adventist Health Study-2. Nutri Metab Cardiovascular Dis. 2013; 23(4): 292-299.
8 Gojda, J., Patkova, J. et al. Higher insulin sensitivity in vegans is not associated with higher mitochondrial density. Eur J Clin Nutr. 2013;67(12): 1310-1315.
9 Satija, A; Bhupathiraju, S.N., Rimm, E.B. et al. Plant-Based Dietary Patterns and Incidence of Type 2 Diabetes in US Men and Women: Results from Three Prospective Cohort Studies. PLOS Medicine 2016.
10 Ahmadi-Abhari, S., Luben, R.N., Powell, N. et al. Dietary intake of carbohydrates and risk of type 2 diabetes: the European Prospective Investigation into Cancer – Norfolk study. Br J Nutr 2014; 111(2): 342-352.
11 Barnard, N.D., Cohen, J., Jenkins, D.J. et al. A low-fat vegan diet improves glycemic control and cardiovascular risk factors in a randomized clinical trial in individuals with type 2 diabetes. Diabetes Care. 2006 Aug;29(8):1777-83.
12 Bernard, N.D., Cohen, J., Jenkins, D.J. 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 May; 89(5): 1588S–1596S.
13 Snowdon, D.A. Animal product consumption and mortality because of all causes combined, coronary heart disease, stroke, diabetes, and cancer in Seventh-Day Adventists. Am J Clin Nutr 1988; 48(3Supp): 739-748.
14 Vang, A., Singh, P.N., Lee, J.W. et al. Meats, processed meats, obesity, weight gain and occurrence of diabetes among adults: Finding from Adventist Health Studies. Ann Nutr Metab 2008; 52(9): 96-104.
15 Tonstad, S., Butler, T., Yan, R., Fraser, G.E. Type of vegetarian diet, body weight, and prevalence of type 2 diabetes. Diabetes Care 2009; 32(5): 791-796.
16 Rizzo, N.S., Sabate, J., Jaceldo-Siegl, K, Fraser, G.E. Vegetarian dietary patterns are associated with a lower risk of metabolic syndrome. The Adventist Health Study 2. 2011. Diabetes Care; 34(5): 1225-1227.
17 van Dam, R.M., Willett, W.C., Rimm, E.B. et al. Dietary fat and meat intake in relation to risk of type 2 diabetes in men. Diabetes Care 2002; 25(3): 417-424.
18 Fung, T.T., Schulze, M., Manson, J.E., Willett, W.C, Hu, F.B. Dietary patterns, meat intake, and the risk of type 2 diabetes in women. Arch Intern Med 2004; 164(20): 2235-2240.
19 Pan, A, Sun, Q., Bernstein, A.M., et al. Red meat consumption and risk of type 2 diabetes: 3 cohorts of US adults and an upturned meta-analysis. Am J Clin Nutr 2011; 94(4):1088-1096.
20 Pan, A., Sun, Q., Bernstein, A.M. et al. Changes in red meat consumption and subsequent risk of type 2 diabetes mellitus: Three cohorts of US men and women. JAMA Intern Med 2013; 1-8.
21 Ley, S.H., Sun, Q, Willett, W.C. et al, Associations between red meat intake and biomarkers of inflammation and glucose metabolism in women. Am J Clin NUtr 2014; 99(2): 352-360.
22 Bloomer, R.J., Kabir, M.M., Canale,R.E. et al. Effect of a 21-day Daniel Fast on metabolic and cardiovascular disease risk factors in men and women. Lipids Health Dis 2010; 9(94).
23 Aune, D.,Ursin,G. et al. Meat consumption and the risk of type 2 diabetes: A systemtic review and meta-analysis of cohort studies. Diabetologia 2009; 52(11):2277-2287.
24 Chiu, T.H., Huang,H.R., et al. Taiwanese vegetarians and omnivores: Dietary composition, prevalence of diabetes and IFG. PLos One 2014; 9(2):e88547.
25 Sheard, N.F., Clark, N.G., Brand-Miller, J.C. et al. Dietary Carbohydrate (Amount and Type) in the Prevention and Management of Diabetes: A Statement by the American Diabetes Association. Diabetes Care. 2004 Sep; 27(9):2266-71.
26 Estadella, D., da Penha Oller do Nascimento, C.M., Oyama, L.M. et al. Lipotoxicity: effects of dietary saturated and transfatty acids. Mediators Inflamm. 2013;2013:137579.