Where are we heading?

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Raymond Simon
5 years ago
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1 Unit 5: Where are we heading? Unit 5: Introduction Unit 1: What s in your food? Unit 2: How does your body use food? Unit 3: What is metabolic disease? Unit 4: How do I identify good and bad food? Unit 5: How does this knowledge apply to me? In the last four units we have learned about the composition of food, digestion and metabolism, metabolic diseases, and how to evaluate nutritional research. This leaves us with the question of how to apply this information to our lives. 180

LESSON 5.1 WORKBOOK How can you use what you know to evaluate claims?

Evaluating nutritional claims So far in this module we have learned a lot about nutrition: from how food is produced to how our bodies use and respond to food after we eat

In Unit 4 we learned about the characteristics and challenges of conducting a nutritional study.

2 LESSON 5.1 WORKBOOK How can you use what you know to evaluate claims? (1) In this lesson we will use the knowledge gleaned from the previous four units to create a toolbox for evaluating nutritional claims and dietary recommendations. Evaluating nutritional claims So far in this module we have learned a lot about nutrition: from how food is produced to how our bodies use and respond to food after we eat it. All of the information that we have learned is based on scientific findings. In Unit 4 we learned about the characteristics and challenges of conducting a nutritional study. Study results are often misinterpreted when being shared with the public, which can lead to nutritional claims or dietary recommendations that are not based on scientific findings. Using the information that we have learned over this module, we can form specific criteria to thoroughly evaluate nutrition claims. Figure 1: The same scientific results should be found multiple times by several scientists to confirm that they are reproducible. 181

Some of these may be scientifically backed, some may be accidental misinterpretations of the science, and some may be intentionally misleading!

3 Figure 2: Nutritional claims or dietary recommendations are commonly found in magazines. Forming a rubric for evaluating a nutritional claim There are many types of nutritional claims that you may come across when you are watching television or reading a newspaper or magazine. Some of these may be scientifically backed, some may be accidental misinterpretations of the science, and some may be intentionally misleading! What you learned in the four previous Units can be used to question the validity of the claim. Unit 1: What s in your food? What nutrient or food is the claim about? Is it a micronutrient or a macronutrient? Is the claim about a purified component of a food (like a supplement), or is it about an entire dietary pattern rich in some nutrients and lacking others? Unit 2: How does your body use food? How is the nutrient or food of interest digested? How is it metabolized? Is the claim consistent with what we know about digestion, absorption and metabolism? Unit 3: What is metabolic disease? How does our body as a whole respond to this food or nutrient? Do we feel full or hungry after eating it? Is there a link between the food or nutrient to obesity and metabolic diseases? Will this lifestyle change alter metabolic rate? Unit 4: How do I identify good and bad foods? Is the claim based on a scientific study? If so, what type of study was it? What kind of conclusions can you make from that type of study? Were all of the confounding variables accounted for? Was there any type of bias? Use the QMDC model to evaluate the study. An example of evaluating a dietary claim Figure 3: If it s an observational study your conclusions are limited. You have learned about the Mediterranean diet in previous units. The typical Mediterranean diet is one that is high in fish, beans, nuts, fruits, vegetables and olive oil, and it is a diet that is lauded for its health 182

4 benefits. This diet is commonly advertised (see Figure 4 below for an example) as being one of the best diets for weight loss, longevity and overall health, but is it healthy for everyone and how were these conclusions derived? Does the science back them up? Figure 4: A news article describes the benefits of an Ancient Greek diet. Are these claims scientifically based? Source: WTOP News After reading the original research article we can determine more about the study referred to in the article and how it was performed. The title of the research article published in The American Journal of Clinical Nutrition is Cretan Mediterranean diet for prevention of coronary heart disease, from which we can already discern that the study was conducted in regards to preventing a type of heart disease. Take a moment to read through the abstract of the article on the next page. 183

5 ABSTRACT: As a result of the Seven Countries Study, the Mediterranean diet has been popularized as a healthy diet. Nevertheless, it has not replaced the prudent diet commonly prescribed to coronary patients. Recently, we completed a secondary, randomized, prospective prevention trial in 605 patients recovering from myocardial infarction in which we compared an adaptation of Cretan Mediterranean diet with the usual prescribed diet. After a mean follow-up period of 27 mo, recurrent myocardial infarction, all cardiovascular events, and cardiac and total death were significantly decreased by > 70% in the group consuming the Mediterranean diet. These protective effects were not related to serum concentrations of total, low-density-lipoprotein (LDL), or high-density-lipoprotein (HDL) cholesterol. In contrast, protective effects were related to changes observed in plasma fatty acids: an increase in n-3 fatty acids and oleic acid and a decrease in linoleic acid that resulted from higher intakes of linolenic and oleic acids, but lower intakes of saturated fatty acids and linoleic acid. In addition, higher plasma concentrations of antioxidant vitamins C and E were observed. We conclude that a Cretan Mediterranean diet adapted to a Western population protected against coronary heart disease much more efficiently than did the prudent diet. Thus it appears that the favorable life expectancy of the Cretans could be largely due to their diet. Am J Clin Nutr 1995; 61(suppl):1360S-7S. Figure 5: Abstract of Cretan Mediterranean diet for prevention of coronary heart disease. For clarification, note that linolenic acid is an omega-3 (n-3) fatty acid, and linoleic is an omega-6 fatty acid. Both types of omega fatty acids are essential, but the Mediterranean diet is especially high in omega-3 fatty acids whereas the Westernized diet is high in omega-6 fatty acid. Oleic acid is the monounsaturated fatty acid that is found in olive oil. Before we can begin to go through our rubric to evaluate the claim that the Ancient Greek diet is the healthiest, we first need to define some terms and determine how the study was conducted. The abstract begins by referring to another study, the Seven Countries Study, which was the original published research that brought the Mediterranean diet into the public eye. The researchers of the current study are focusing on a specific type of Mediterranean diet that is consumed by people living on the Greek island of Crete, a diet called the Cretan Mediterranean diet. The participants of this study were people living in a Westernized culture that were recovering from a myocardial infarction (heart attack), and the study was conducted in France. Study participants were randomly assigned to either receive dietary counseling about the Cretan Mediterranean diet (the experimental group), or to receive the dietary recommendations that are standard after hospitalization for a heart attack (the control group). 184

The Cretan Mediterranean diet that was recommended to the experimental group consisted of The Six Dietary Commandments : 1. More bread. 2. More vegetables and legumes. 3. More fish. 4.

The researchers end goal was to determine whether the Cretan Mediterranean diet could prevent another heart attack, cardiovascular event or death.

6 The Cretan Mediterranean diet that was recommended to the experimental group consisted of The Six Dietary Commandments : 1. More bread. 2. More vegetables and legumes. 3. More fish. 4. Less meat (beef, lamb, pork) and replaced by poultry. 5. No day without fruit. 6. Replaced butter and cream with a special oil-based margarine that has similar fatty acid types to olive oil. The researchers end goal was to determine whether the Cretan Mediterranean diet could prevent another heart attack, cardiovascular event or death. They used measurements of LDL, HDL, and blood concentrations of the essential fatty acids to determine if the two diets resulted differences in the participants. Using the rubric to evaluate the Ancient Greek diet Now let's walk through the rubric we formed to evaluate the nutritional claim that the Ancient Greek diet is the healthiest diet. Unit 1: What s in your food? This claim is regarding a total diet, namely the Ancient Greek, or Cretan Mediterranean diet. The diet in the news article is rich in fish, vegetables, fruits and, above all olive oil. Figure 6: Crete (in red) is a Greek island south of the mainland. Figure 7: The Cretan Mediterranean diet is high in bread, fruits, vegetables and fish. 185

7 Unit 2: How does your body use food? The Mediterranean diet that is described by the news article would be high in omega-3 fatty acids from the fish, monounsaturated fatty acids from the olive oil, as well as fiber, and micronutrients from the fruits and vegetables. Both omega-3 and monounsaturated fatty acids are important for building cell membranes and maintaining normal cellular functions. Also, because the saturated fat intake is low, the HDL to LDL ratio in the blood may increase, which we know is correlated with a low risk of heart disease. Additionally, soluble fiber from the vegetables and fruits can absorb bile from the intestines so that it is excreted in the feces. Remember that bile is made of cholesterol; therefore eating soluble fiber can decrease your body s total cholesterol levels. Unit 3: What is metabolic disease? Eating a diet rich in fat, protein and fiber makes us feel full for a longer period of time than eating a highly processed diet rich in simple carbohydrates. The Mediterranean diet is high in fat, protein and fiber, so an overall decrease in calories consumed is possible if the diet is strictly adhered to. However, the dietary recommendations for the experimental group do not limit calorie intake, so weight loss may not be expected. This diet is also low in sweet foods, so the reward pathway will not be activated as fully as it would when we eat our favorite sweet and fatty foods. Food cravings for sweet foods may be present while eating this diet, perhaps leading to more snacking and increased calorie consumption. Unit 4: How do I identify good and bad foods? Now let's use the QMDC method to walk through the published scientific article that is referred to in the news piece. The BIG Question was whether a Cretan Mediterranean diet could prevent coronary heart disease better than a standard diet prescribed to patients who have had a heart attack. The Method used was a randomized controlled study, though it was not double-blinded because the participants knew what type of diet they were following. Because this was an interventional study, causative results and conclusions can be made, but be careful! We must determine if all types of biases were accounted for. Is there selection bias? Information bias? A confounding variable? Notably, this study had participants with a history of heart disease, which may impact the types of conclusions you make. Observational Interventional Correlation Causation Figure 8: The type of study determines the extent of the conclusions you could make. 186

8 The Data are shown in tables and figures throughout the scientific article, two of which are presented below. The first table shows the comparison of nutrients eaten in the control and experimental groups. Nutrients that had the largest differences between groups are shaded in red. What conclusions can you make using the table? Were the two diets rich in different nutrients? Is the difference in diets meaningful or just measurable? Intake of nutrients in the experimental and control groups a6er 1-4 years Control Group Experimental Group Total Energy (kcal) 2152 ± ± 7920 Percent of energy (%) Protein 16.6 ± ± 0.3 Total lipids 33.1 ± ± 0.5 Saturated fat 11.8 ± ± 0.2 Monounsaturated fat 10.4 ± ± 0.3 Linoleic Acid 5.4 ± ± 0.1 Linolenic Acid 0.28 ± ± 0.03 Vitamin A (ug) 548 ± ± 72 Vitamin C (mg) 101 ± ± 4 Vitamin D (ug) 2.8 ± ± 0.2 Vitamin E (mg) 13.6 ± ± 0.3 Cholesterol (mg) 320 ± ± 11 Figure 9: Table adapted from Cretan Mediterranean diet for prevention of coronary heart disease showing the differences in macro and micronutrients between the two diets. Nutrients shaded in red are significantly different in the two groups. The graph in Figure 10 (see next page) shows the number of study participants in both the experimental and control groups that did not have an 'event', which is either a heart attack, death from heart attack, stroke or a blood clot from atherosclerosis. The Data shows that the experimental group had far fewer 'events' than the control group. 187

9 Finally, using the Data we can make some Conclusions. The experimental diet presented in this scientific article did seem to contain different macro and micronutrients than the control diet. As mentioned in the abstract, the experimental group had high omega-3 fatty acids and lower omega-6 fatty acids in their blood compared to the control group. Overall, the experimental group had less cardiovascular events, and the Cretan Mediterranean diet protects against heart disease more efficiently than the control diet in a population that has already suffered a heart attack. From this data would you agree that the Ancient Greek diet is the healthiest diet for everyone? If we were to only use the study discussed here as evidence, would it be difficult to argue that a healthy person can benefit from following the Ancient Greek diet, or does the conclusion seem solid? Population without event! Experimental! Control! Years after randomization! Figure 10: Figure from Cretan Mediterranean diet for prevention of coronary heart disease illustrating the proportion of each population that has not had a cardiovascular event. 188

10 STUDENT RESPONSES List three alternative explanations to explain the results in figure 10. To form your answer, consider who the study participants were, what type of study was conducted, what the treatment and control groups were, how long the study was conducted, and what measures were made. Remember to identify your sources 189

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