Carbs: The Staff of Life, or The Stuff of Death? Ed Cox, M.D.

Carbs: The Staff of Life, or The Stuff of Death? Ed Cox, M.D.

Pyramid, or Paleo?

Carbs defined Carbohydrates (abbrev. CHO) = saccharides Saccharide from Greek for sugar Compounds of carbon, oxygen and hydrogen in the ratio of 1:1:2, for example, C6O6H12 (glucose) Polymers of the simplest unit, a monosaccharide The polymers are disaccharides (2 units), oligosaccharides (39), and polysaccharides (>9) Monosaccharides and disaccharides are, mostly, sugars Polysaccharides from plants are starches or cellulose

Monosaccharides Common monosaccharides in nutrition are glucose, fructose and galactose Glucose: grape sugar Fructose: found in many plants, in cane sugar Galactose: found in milk sugar Monosaccharides resulting from digestion of starches are absorbed in small intestine Monosaccharides can exist in a closed form and an open form Closed form predominates and is the form that is polymerized to make di-, oligo- and polysaccharides Glucose is the most important monosaccharide, as it is the common transport and storage saccharide Polymerized into glycogen in the liver and muscles for storage Released from storage as the body calls for energy

Disaccharides Disaccharides consist of two monosaccharides Generally perceived as sweet tasting Sweet monosaccharides and disaccharides are known as sugars Common disaccharides Sucrose: Glu-Fru cane sugar Lactose: Gal-Glu milk sugar Maltose: Glu-Glu released in breakdown of starch

Oligosaccharides Oligosaccharides are short polymers of about 3 to 9 monosaccharides Important ones come from plants Those that are non-digestible and non-absorbable may play important roles as nutrients for intestinal microflora Concept of prebiotics substances that keep our intestinal tract micro-organisms in the right balance Some may play a role in irritable bowel disease, gluten intolerance

Polysaccharides Polysaccharides are long chain polymers of monosaccharides (generally > 10 units) Most important PS are polymers of glucose Animal: Glycogen, the storage PS Plants: Starch (amylose and amylopectin) and cellulose

Cellulose Most abundant organic polymer on Earth Main structural component of plants 40-50% of wood, 45% of hemp, 90% of cotton Long straight chains of glucose which are cross-linked to adjacent chains, in a very dense, strong network Digestible only by ruminants, termites

Digestion of polysaccharides Amylose and amylopectin are PS found in fruits of plants; known as starch Amylase (lower image) is the enzyme that cleaves amylose and amylopectin into mono-, di- and oligosaccharides Amylopectin (70-80% of starch) is digested rapidly, into maltose and glucose Amylose (20-30% of starch) is digested slowly, into maltose and oligosaccharides; resistant starch

Plant fruit Fruit in this context refers to the part of a plant which allows its reproduction Kernel, in cereals Nut, in trees Seed, in other plants Endosperm is the starch that provides fuel as a plant germinates, before it can gather energy through photosynthesis The fruit is the part that is readily used for animal nutrition Grinding, cooking, etc. partially disrupt the starch to make it more digestible

Digestion of CHO Amylase in the saliva begins to break down starch and glycogen in food into monosaccharides and oligosaccharides as food is chewed in the mouth Amylase continues to act on the food in the stomach, and additional amylase is added as digesting food enters the small intestine Lactase is a special enzyme for splitting lactose into glucose and galactose; sucrase splits sucrose into glucose and fructose Monosaccharides and maltose are absorbed directly by the small intestinal lining

Glucose and insulin Insulin is the master control molecule to maintain constant blood sugar level Secreted by pancreas islet cells Signals liver and muscles to remove glucose from blood

24 hour glucose and insulin

Post-meal glucose and AUC Blood glucose expressed as mmol/l (mg/dl) Baseline 4.5 mmol / L (80 mg/dl) After 50 g of oral glucose: Peaks about 3.5 (63) above baseline at 30 min Returns gradually to baseline at 100 min Similar to oral glucose tolerance test (GTT) AUC (area under the curve) is measured as a standard for comparison with other foods AUC for glucose here is 150 mmol/l-min Reflects the balance between glucose absorption and its use or storage under the influence of insulin

Hyperglycemia Refers to blood glucose values that rise substantially above those in healthy individuals after a meal, or remain elevated after digestion is complete Hyperglycemia is the defining characteristic of diabetes mellitus Type I diabetes is complete failure of insulin secretion by the pancreatic islet cells; earlier referred to as juvenile diabetes Type II diabetes is insufficient insulin secretion relative to the metabolic need for it Major component of metabolic syndrome, or syndrome X Associated with obesity, hypertension Associated with lipid abnormalities, increased risk of CHD, CVD Earlier referred to as adult-onset diabetes

Quantifying hyperglycemia Long known that the persistent blood sugar elevation is associated with dramatic increase in cardiovascular diseases Suspected that the elevated blood glucose itself was strong contributor to vascular disease Further suspected that elevated blood glucose levels not high enough to make a diagnosis of diabetes could be harmful Different carbohydrates produce different blood glucose profiles after their consumption Needed a measure for quantifying the amplitude and duration of glucose elevation

Glycemic index concept Developed by David Jenkins, M.D., Ph.D. (Nutrition), at University of Toronto, in early 1980s GI defined as the ratio of two areas under the glucose vs. time curve above the baseline glucose level: 1) specified amount of test CHO (usually 50 g); 2) same amount of glucose Used to test a large variety of CHO foods in healthy subjects to determine their GI Used to correlate the GI of individual diets with health outcomes, such as chronic diseases like diabetes and CHD

Glycemic index illustrated One peaks about 2.3 (40) above baseline at 30 min AUC for white breads are 114, 95, 74 for high, medium and low GI, and 150 for glucose Another peaks about 2.2 (36) at 30 min GI = 100*AUCfood/AUCglucose A third peaks about 1.9 (29) at 30 min Returns gradually toward baseline at 120 min After 50 g of different white breads: AUC is measured for each bread for comparison with glucose and divided by AUC for glucose GI for bread are 76, 63, and 49 Reflects how well insulin secretion is matched to glucose absorption to maintain glucose level close to normal

Glycemic index general findings Highest glycemic index foods (>70) are white bread, white rice, potato, refined breakfast cereals, bagels, pretzels, glucose, maltose Lowest glycemic index foods (<55) are vegetables, most fruits, most intact whole grains, seeds, beans, nuts Intermediate GI foods are processed whole grain, pasta, sucrose, banana, converted rice However, many other factors enter in, so each food by each manufacturer and different cooking methods must be tested individually For example, whole wheat bread can have a high GI or a low GI, depending on exact manner in which it is prepared; rice has great variation depending on type, processing and cooking

Glycemic index - detailed

Glycemic load Which is better - a small amount of a high GI food or large amount of a low GI food? They give essentially the same AUC So, another measure is needed that incorporates both GI and amount of food That measure is the glycemic load, the product of GI of the food times the amount of CHO in the food on a given day, divided by 100 Example: A serving of potato containing 100 g of CHO that has a GI of 80 has a glycemic load of 100 x 80 / 100 = 80

Does the GI tool work? Do glycemic index and glycemic load give us a real handle on what carbs are good for us and which we should avoid? GI/GL has good rationale, since it relates to hyperglycemia in people with diabetes and metabolic syndrome, and the consequences However, is it really predictive of outcomes, especially in apparently healthy individuals?

Sugary drinks and CHD Fung et al Am J Clin Nutrition 2009

Sugary drinks and CHD - NHS Nurses Health Study 88,520 women ages 34-59 No pre-existing CHD, stroke, CVD, or diabetes Detailed, repeated dietary histories Detailed accounting for confounding variables Follow-up of 24 years, during which 3,105 cases were observed (MI or death from CVD)

Sugary drinks and CHD - NHS

Sugary drinks and CHD - NHS

Sugary drinks and CHD - NHS

Sugary drinks and CHD NHS Artificial sweeteners

Glycemic load and CHD Liu et al Am J Clin Nutrition 2000

Glycemic load and CHD - NHS Nurses Health Study 75,521 women ages 38-63 No pre-existing CHD, stroke, CVD, or diabetes Detailed, repeated dietary histories Detailed accounting for confounding variables Follow-up of 10 years, during which 761 cases were observed

Glycemic load and CHD - NHS Explanatory variables examined Total amount of carbohydrate Amount each of starch, sucrose, fructose and lactose Glycemic load Glycemic index (glycemic load / total carb) Interaction with fat intake, BMI

Glycemic Load Effect on CHD by Body Mass Index

CHO & CHD Risk - Conclusions Total CHO, amount of starch, and amount of sugar per day are not associated with CHD risk But CHO, characterized by glycemic index and glycemic load, are highly associated with CHD Glycemic index 31% incr. CHD, Q5 vs. Q1 Glycemic load 98% incr. CHD, Q5 vs. Q1

CHO & CHD Risk - Conclusions High glycemic load diet does not increase risk in subjects with lower BMI, moderately increases risk in middle BMI and greatly increases risk in higher BMI individuals Consistent with observations that insulin resistance and CHO-induced hyperlipidemia are greatest in higher BMI individuals

CHO & CHD Risk - Restated Undisciplined CHO intake ranks among the most destructive possible personal habits, especially in susceptible individuals New information recognizes low salivary amylase as potential risk factor for obesity and metabolic syndrome / diabetes CHO can safely and effectively provide the majority of energy required to support an active life, provided: You favor low glycemic index CHO foods You limit amounts of high glycemic index CHO foods You keep your body mass index in a reasonable range You don't have an inherited metabolic tendency to produce abnormal quantities of undesirable lipids