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Insulin…it’s not just a pill for treating diabetes.

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Insulin…it’s not just a pill for treating diabetes

Insulin is a hormone that has many effects on metabolic and cellular processes in the tissues and organs of the body. Insulin’s main action is to stimulate the uptake of glucose (from meals) into skeletal muscle and the heart and to inhibit the production of glucose and triglycerides in the liver. Insulin regulates the metabolism of carbohydrates, proteins, and fats after a meal and promotes cell growth.

If we consume too many calories, the excess glucose is converted by the liver to free fatty acids. These free fatty acids (FFAs) are transported as triglycerides in lipoproteins called very low-density lipoproteins (VLDLs), through the blood, and deposited in our adipose (fat) tissue.

An excess of free fatty acids has been associated with insulin resistance because it is believed to impair the insulin-signaling pathway. While insulin sensitivity is the ability of insulin to signal body tissues to take up and utilize glucose and inhibit FFA formation in the liver, insulin resistance results when this sensitivity is impaired and normal levels of insulin in the body no longer signal the absorption of glucose into the tissues. The results is an excessive level of insulin the blood trying to maintain normal blood glucose levels.

One of the main consequences of excess food intake leading to chronic insulin resistance is inflammation, which is the body’s natural defense mechanism when it encounters toxins. Besides excess calories, a large part of this inflammation is thought to be due to the intake of certain types of fats in our diet; in particular omega-6 fatty acids and saturated fats (especially arachidonic acid and palmitic acid). These fats are considered pro-inflammatory because they lead to insulin resistance. Other fats, such as omega-3 fatty acids, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are considered anti-inflammatory, as they can decrease insulin resistance.

Intake of saturated fats (palmitic acid in particular) or excess calories in general can lead to a decrease in satiety cues, giving us the feeling of fullness after a meal) coming from the hypothalamus region of the brain, which then leads to an increase in hunger and intake of more calories. The hypothalamus has binding proteins for omega-3 fatty acids such as EPA and DHA, meaning intake of these fats can decrease inflammation. The hypothalamus also has receptors for the omega-9 fatty acid oleic acid. When oleic acid is consumed, it binds to receptors in the hypothalamus and leads to satiety, which normally triggers us to stop ingesting more calories.

The best place for the body to store excess fat calories is the adipose (fat) tissue which can expand and store excess intake as triglycerides. Fat cells, however, do not have a limited capacity to expand, and once these fat cells have expanded to their limit, they essentially become starved of oxygen, leading to inflammation and later insulin resistance. This in turn can lead to FFA release from fat cells to the circulation and uptake by other organs such as the liver or skeletal muscle which are not able to safely store large amounts of fat. This in turn leads to insulin resistance in these organs.

The build-up of FFAs in the liver is known as non-alcoholic fatty liver disease (NAFLD). Approximately 30% of Americans and 90% of obese individuals with type 2 diabetes have NAFLD. Someone may be obese from excess intake and have no insulin resistance if the fat cells have not yet reached the point of over-expansion. Nonetheless, insulin resistance in the liver is related to FFAs in the liver, not in visceral fat, the fat around our abdomen. This is thought to explain why some normal weight individuals are found to have insulin resistance in the liver. Even in normal weight individuals, this insulin resistance can lead to increased levels of VLDLs (TGs) and decreased levels of HDL cholesterol, the “good” cholesterol which carries cholesterol from the body to be processed in the liver and then flushed out of the body.

Insulin resistance in the adipose tissue leads to excess fat being released into the bloodstream and taken up by the liver and skeletal muscle tissue which are not able to handle this excess fat. As a result, normal metabolic functions are inhibited. This leads to the development of such chronic conditions associated with insulin resistance, including type 2 diabetes, heart disease, and polycystic ovary syndrome.

As we can see, the types and amounts of fats in our diet have a very important role in the development or suppression of insulin resistance. So, how do we translate that to nutrition advise? What foods should we eat, and which should we avoid so that we steer clear of these inflammatory fats which can lead to overindulgence and insulin resistance?

Foods highest in inflammatory saturated fatty acids are:

  1. Palm oil
  2. Vegetable shortening and lard
  3. Butter, both salted and unsalted
  4. Pork
  5. Beef
  6. Rice bran oil
  7. Egg yolks
  8. Chicken
  9. Cream from milk fat
  10. Potato chips (often made with palm oil and other inflammatory oils)

Fish such as salmon, trout, and tuna are high in omega-3 fatty acids. For those who have a fish allergy or choose to avoid fish, many plant foods are also excellent sources of omega-3 fatty acids.

Plant foods highest in anti-inflammatory omega-3 fatty acids and polyunsaturated fat from oleic acid are:

  1. Chia seeds
  2. Hemp seeds
  3. Walnuts
  4. Flaxseeds
  5. Flax oil
  6. Avocados
  7. Cashews
  8. Almonds
  9. Pistachios
  10. Hazelnuts

We now know that not all fats are equal and the fats we choose to eat can have significant consequences to our body functions and risk for developing chronic conditions such as diabetes and heart disease.

Check out some of my recipe videos featuring these foods rich in omega-3s and oleic acid.

References:

  1. Sears B, Perry M. The role of fatty acids in insulin resistance. Lipids in Health and Disease. 2015. 14:121
  2. Jellinger P. Metabolic Consequences of Hyperglycemia and Insulin Resistance. Clinical Cornerstone. Glucose Dysregulation. 2007. 8(7):S30-S42.
  3. Wilcox G. Insulin and Insulin Resistance. Clinical Biochemist Review. 2005. 26:19-39.
  4. What’s In the Foods You Eat. US Department of Agriculture. Agricultural Research Service. Accessed from https://reedir.arsnet.usda.gov/codesearchwebapp/(S(5ltc3grjhrnhogdz5boylvni))/CodeSearch.aspxon 07/19/2020.
mixed food meal

What Does Insulin Have to Do with Cancer Recurrence?

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Healthy diet and physical activity have been shown by evidence-based research to decrease risk of certain cancers. Studies also shows that these factors can affect cancer recurrence and survival, as researchers at the Dana-Farber Cancer Institute in Boston, MA found. More interestingly, as these researchers point out in their study on colon cancer recurrence and survival, insulin spikes occurring after a meal may be linked to greater cancer mortality.[1]

So, what does insulin have to do with cancer recurrence? We know that a carbohydrate-rich diet can induce hyperinsulinemia, an increase in insulin secretion into the blood. Foods with a high dietary glycemic load or glycemic index, meaning those that increase blood sugar more than other foods, have been linked to worse patient outcomes in those with stage III colorectal cancer. However, the glycemic load looks only at the increase in insulin secretions in response to carbohydrates only and does not consider the insulin spike associated with protein- and fat-rich foods. Protein and fats also stimulate the secretion of insulin into the blood and, as the researchers explain, protein and fats act in conjunction with carbohydrates. Therefore, it is important to look at the effect of protein and fats as well as carbohydrates, on insulin spikes. 

The Food Insulin Index, in contrast with the Glycemic Index, measures the insulin spikes after consumption of whole meals or individual foods with carbohydrates, protein, and fats.[2] The researchers used this information to assess how insulin levels in the blood after meals affect cancer recurrence and survival in patients who have had a tumor resection after diagnosis with Stage III colorectal cancer. 

The study utilized validated food frequency questionnaires to assess the diets of 1023 patients.  Statistical methods involved multivariable-adjusted analyses and Cox proportional hazards regression to adjust for possible confounders such as age, sex, body mass index (BMI), physical activity, cereal fiber intake, alcohol intake, and invasiveness of the colorectal cancer. 

The study found that higher insulin load (greater quantity of the foods measured) and higher insulin index were linked to increased risk of colorectal cancer recurrence and mortality. This association remained, even after adjusting for glycemic index, indicating that certain protein- and fat-rich foods may lead to insulin secretion and affect cancer outcomes. 

In other words, we may need to look beyond carbohydrates for associations between diet, insulin levels, and cancer outcomes. After all, people typically eat meals and snacks throughout the day with a mixture of carbohydrates, protein, and fats – not carbohydrates alone, protein alone, or fats alone. The researchers considered this a strength in their study, since the consumption of mixed meals with more than purely carbohydrates are more realistic because carbohydrates, protein, and fats work together to stimulate the secretion of insulin. 

Foods that result in a greater insulin index were determined by tables created by Dr. Brand Miller and other researchers in Sydney, Australia.[2,3] The reference food was white bread with a food insulin index (FII) score of 100. The tables compare equal weight portions (in grams) as well as portions of foods that provide equal numbers of calories. Among comparisons of foods of equal portions (in grams), some protein-rich foods such as beef, fish, eggs, and cheese were found to have a greater FII than carbohydrate-rich foods, such as refined wheat pasta or whole wheat pasta.  

The colorectal cancer study found that an overall diet that greatly increases insulin levels in the blood is associated with poorer cancer outcomes – cancer recurrence or death – whether the patient was overweight or obese and regardless of the patient’s level of physical activity. 

The researchers recognized the strict criteria and motivation needed to be enrolled in and participate in their study as a potential limitation. Nonetheless, they did not find statistically significant differences in the diet between their study participants and the diet of the general population. 

This research shows us that dietary choices have a strong influence on colorectal cancer outcomes. From the Food Insulin Index tables and ongoing research, we must acknowledge the importance of our overall diet, not just certain foods alone. Equally important, we must acknowledge the importance of the types of carbohydrates and types of protein-rich or fat-rich foods we eat, and not try to eliminate entire nutrients – carbohydrates or fats, for example – from our diets.

Food Insulin Index Tables can be found on the Harvard T.H. Chan Public Health Nutrition File Download page, and in the studies by Bao, et al, [2] and Holt, et al.[3]

References

  1. Morales-Oyarvide V, Yuan C, Babic A, et al. Dietary Insulin Load and Cancer Recurrence and Survival in Patients with Stage III Colon Cancer: Findings From CALBG 89803 (Alliance). Journal of the National Cancer Institute. 2019, 1-9
  2. Bao J, de Jong V, Atkinson F, et al. Food insulin index: physiologic basis for predicting insulin demand evoked by composite meals. American Journal of Clinical Nutrition. 2009, 986-992
  3. Holt S, Brand Miller J, Petocz P. An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods. American Journal of Clinical Nutrition. 1997, 1264-1276
  4. Harvard T.H. Chan School of Public Health, Nutrition Department, File Download Page, found at https://regepi.bwh.harvard.edu/health

High Carb Diet for Diabetes?

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With low carb and ketogenic diets achieving so much attention, let’s take a look at some of the data on high carbohydrate diets and their effects on one of the most problematic chronic diseases facing the globe; type 2 diabetes.  

High carbs for diabetes? But, aren’t those with type 2 diabetes usually told to avoid carbs? Sure, but the type and quality of the carbohydrate is crucial.

Again, let’s look at the science. 

As we have seen, low carb diets have some small positive benefits, but also raise some negative consequences that should not be ignored and undoubtedly need to be studies more in depth.

We can go back as far as 1935 to see the effects of a high carb diet in a study conducted by Rabinowitch.[1] Why look at data from decades ago? Studies like this show how long we have had the backbone of research on beneficial diets to treat diabetes, yet we still look for ways to “beat the system!” Maybe that proves the power of Big Food lobbies to influence what’s on our plate…

Rabinowitch found that high carb low calorie diet led to lower insulin requirements than all other diabetics diets interventions tried at the time. His study was based on the known fact that carbohydrates improve carbohydrate tolerance and insulin sensitivity while fats impair carbohydrate tolerance and insulin sensitivity. After placing 50 subjects on the intervention diet over 5 years, average daily insulin dosages dropped from as much as 60 units to 10.6 units. In 12 subjects, insulin was discontinued altogether on the high carb low calorie diet. 

Was it just the calorie restriction that led to better glycemic control? How about a high carb diet that provides as many calories as a lower carbohydrate control diet?

A 1979 study compared a high carb high fiber intervention diet (70% CHO, 21% protein, 9% fat) against a lower carb control diet (43% CHO) providing the same number of calories.[2] Both diets were vegetarian, and included milk but no eggs. To control blood sugar levels, daily doses of insulin needed were significantly lower for all subjects on the high carb high fiber diet than on the control diet. In most subjects, insulin doses were decreased after as little as 3 days on the diet. Fasting plasma blood glucose levels were lower for most subjects on the high carb high fiber diet despite receiving lower insulin doses. Cholesterol levels dropped nearly 60 points in the high fiber diet pattern. Interestingly, however, the changes in insulin doses needed and blood sugar levels were comparable regardless of the fiber content of the diet. The changes were therefore most likely attributed to the carbohydrate content of the diets. And, importantly, when subjects on the high carb high fiber intervention diet returned to conventional diet lower in carbs and fiber, their insulin doses increased to levels seen in the control diet. 

More recently, researchers compared a vegan diet consisting of fruits, vegetables, grains, legumes, and no portion restrictions, providing 75% of calories from carbohydrates against an omnivorous diet which allowed low-fat animal products based on the American Dietetic Association (ADA) diet principles, providing 60-70% of calories from carbohydrates with minimal saturated fat and cholesterol.[3] The study aimed to determine which diet was more effective for controlling type 2 diabetes. The majority of the study subjects were obese or overweight and both diets involved calorie reduction. After 22 weeks, the subjects following the vegan diet lost 13 lbs while those on the ADA diet lost less than 10 lbs. Among the most medically-stable subjects who needed no diabetes medication changes, the vegan group lost even more weight and the control group lost less weight. HbA1C levels (which tells clinicians someone’s average blood sugar reading over the previous 3 months) were reduced in both groups, but the impact seen in the vegan diet group was more than 3 times greater. LDL cholesterol levels fell more than 21% among the vegan group and less than 11% in the ADA group. Among the medication stable subjects, HbA1C, LDL  cholesterol levels, weight, and waist circumference are decreased more significantly among subjects following the vegan diet. 

In this study, both the low-fat vegan diet and the portion-controlled ADA diet were successful in lowering blood sugar and cholesterol levels. However, the improvements were more pronounced with the low-fat vegan diet. 

Vegan diets are cholesterol-free, low in saturated fat, and high in soluble fiber, which has a cholesterol-lowering effect. And, as the study authors point out, this is an important point because cardiovascular complications are the main cause of morbidity and mortality among those with type 2 diabetes. 

With over 10% of Americans diagnosed with T2DM[4], more attention needs to be given to diet and diet composition. A registered dietitian nutritionist can work with you to create the diet that works best for you. Either way, feel good knowing you can tell your friends that the risks of the keto diet outweigh the benefits long term. so you’re making a smart choice avoiding the low-carb keto bandwagon. 

Citations:

1. Rabinowitch, I. M. Effects of the High Carbohydrate – Low Calorie Diet Upon Carbohydrate Tolerance in Diabetes Mellitus. Canadian Medical Journal., 1935,136-144

2. Anderson J, Ward K. High-carbohydrate, high-fiber diets for insulin-treated men with diabetes mellitus. (1979) American Journal of Clinical Nutrition 32:2312-2321

3. Barnard N, Cohen J, Jenkins D, 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. (2006) Diabetes Care 29(8) 1777-1783

4. National Diabetes Statistics Report, 2020. Centers for Disease Control and Prevention. 2020. https://www.cdc.gov/diabetes/library/features/diabetes-stat-report.html accessed on June 21, 2020

Avant Carb!

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Should You Try A Low Carbohydrate Diet?

Many people are adopting a so called “low-carb diet” in an attempt to lose weight. Are diets low in carbohydrates – the main source of energy for our bodies – actually safe? 

A diet low in carbohydrates usually allows for non-starchy vegetables like kale, spinach, and peppers. Fantastic; these are powerful nutrient-packed foods. And, sure, it’s wise to avoid refined processed products such as breads and pastries, and many commercial grain-based breakfast cereals which are stripped of intact fibers and minerals. However, a diet low in carbohydrates also means a diet low in whole grains, most fruits, starchy vegetables, beans, and lentils. Once you limit carbohydrates, the remains macronutrients to focus on are fat and protein. The diet usually allows for nuts and avocados, which are high in protein and unsaturated fat – great! – but you may end up getting most of your protein and fat from animal sources, which usually results in too much saturated fat. 

Low carb diets are often designed to deprive the body of glucose for energy and induce a metabolic process called ketosis to burn fat cells. 

Should we really be avoiding so many of the healthiest foods on the planet which are also rich sources of antioxidants, fiber, vitamins, minerals, powerful protein, and phytonutrients? 

Let’s see what the science tells us. 

Noto, et al conducted a review and meta-analysis of studies looking at the effects of low carb diets on cardiovascular disease risk factors. The researchers found low carb diets were associated with a significantly greater risk of all cause mortality.[1] They found that while some studies included in their analysis showed low carb diets were not relevant in terms of cardiovascular disease, subgroup analyses did show low carb diets may increase the risk of CVD and mortality when the diet follows an animal-based pattern and they may decrease such risks in plant-based diet patterns.

Samaha et al found that in morbidly obese individuals (BMI >40), low carb diets induced more short term weight loss than low fat diets.[2] However, the amount of weight lost was small and the study duration was only 6 months. 

Another meta analysis conducted by Bueno, et al studied the effects of a very low carbohydrate ketogenic diet and how it compared to a low-fat diet for long term weight loss. Bueno et al found that very low carbohydrate diets were indeed more effective at reducing body weight, and even increased HDL (good) cholesterol.[3] However, the diet was found to increase levels of LDL (bad) cholesterol levels, which the author points out, was likely due to the diet’s high content of saturated fat. 

In response to this study, researchers in Vienna, Austria conducted a study (also a meta-analysis of randomized controlled trials) to look at the effects of low carb (<45% kcal from CHOs) and low fat (<30% kcal from fat) diets and their effects on endothelial function, a known independent risk factor for atherosclerosis and other markers of cardiovascular disease.[4] This study found that markers of endothelial function were significantly more reduced in those following a low carb diet than in those following low fat diets.

Given the potential for increased mortality, increase in LDL cholesterol, and small amounts of weight loss seen after 6 months may not be a good enough reason to ditch the whole grains, sweet potatoes, and black beans.

After all, people don’t eat carbohydrates – have you ever seen a carbohydrate tree or carbohydrates for sale in the supermarket? No, because people eat foods which contain varying amounts of carbohydrates, amino acids, fats, micronutrients, and phytonutrients, etc. We may be wiser to pay attention to the sources of carbohydrates (think oatmeal versus donuts) and the sources of protein (think black beans versus steak).

Until we have more concrete evidence on the efficacy and safety of low carb diets, let’s focus on what the science says about the effects of high carb diets and disease outcomes.

Citations:

  1. Noto H, Goto A, Tsujimoto T, Noda M (2013) Low-Carbohydrate Diets and All-Cause Mortality: A Systematic Review and Meta-Analysis of Observational Studies. PLoS ONE 8(1): e55030. doi:10.1371/journal.pone.0055030
  2. Samaha F, Iqbal N, Seshadri P, et al (2003) A Low-Carbohydrate as Compared with a Low-Fat Diet in Severe Obesity. New England Journal of Medicine 348:2074-81
  3. Bueno, N., De Melo, I., De Oliveira, S., & Da Rocha Ataide, T. (2013). Very-low-carbohydrate ketogenic diet v. Low-fat diet for long-term weight loss: A meta-analysis of randomized controlled trials. British Journal of Nutrition, 110(7), 1178-1187. 
  4. Schwingshackl, L., Hoffmann, G. University of Vienna. (2013) Letter to the Editor. Low-carbohydrate dies impair flow-mediated dilation: evidence from a systematic review and meta-analysis. British Journal of Nutrition (2013) 
legumes grains