A healthy diet has numerous benefits. But what does a healthy diet consist of? And how do we, researchers, measure diet quality?

What’s considered a healthy diet in one country or culture, may not be regarded as such in another. For instance, low-fat and unsweetened dairy products are regarded as healthy in my country, the Netherlands, but not in many Asian countries where a vast proportion of the population is lactose intolerant. Differences in regional availability of foods further determine dietary habits across, and even within, countries. Fish, for example, is often at the core of a healthy diet in countries surrounded by water such as Japan (48.6 kg/year per person), but not in landlocked countries such as Hungary (5.1 kg/year per person) [1].

Here I will describe six common ways in which researchers may assess diet quality in Western populations.

1. Fruit and Vegetable Consumption

Probably the quickest way to obtain an estimate of an individual’s diet quality is by assessing fruit and vegetable consumption of the individual. Generally speaking, fruits and vegetables are high in healthy nutrients such as vitamins and fibers. Moreover, fruits and vegetables often replace unhealthier options such as energy-dense snacks. Finally, while fruit and vegetable consumption is only one aspect of diet quality, it has been shown to correlate with overall diet quality. Thus, fruit and vegetable consumption can be seen as a fast but crude way to assess diet quality.

2. Total Energy Intake

One could consider calculating total energy intake as an indicator of diet quality. Generally speaking, unhealthy foods are more energy-dense than healthy foods. Therefore, high-calorie diets likely contain more unhealthy foods. Of course, this is not necessarily the case; some foods, for instance avocado, are both energy-dense and nutrient-rich. Moreover, low energy intake may result in nutritional deficits. Therefore, total energy intake is not generally used as an indicator of diet quality.

3. Mediterranean Diet Score

The Mediterranean Diet Score (MDS) measures compliance to a Mediterranean-type diet, consisting of legumes, fruits, vegetables, unrefined cereals, olive oil and fish. Points are subtracted for dairy and meat [2]. The Mediterranean diet was inspired by the eating habits of Greece and Italy, where people seem to live longer and have lower risk of heart disease compared to other Western regions.

4. Western-Type Diet Score

A Western-style diet is a modern dietary pattern, that is sometimes referred to as the Standard American Diet. A Western diet consists of red and processed meats, pre-packaged foods, fried foods, whole-fat dairy products, refined grains, potatoes and sugar-sweetened beverages, among others [3]. Contrary to most diet quality scores, a higher Western diet score indicates a less healthy diet.

5. Healthy Eating Index

The Healthy Eating Index (HEI) measures how well an individual adheres to the key recommendations of the 2015 Dietary Guidelines for Americans. These guidelines are often used by US-based nutrition and health professionals, to help people to consume a healthful and nutritionally adequate diet. A total score is calculated based on nine advised food groups/components (including fruits and vegetables, whole grains, plant proteins), and four components that should be moderated (including salt and saturated fat) [4].

6. Dietary Approaches to Stop Hypertension

The dietary approaches to stop hypertension (DASH) dietary pattern emphasizes fruits, vegetables, low-fat dairy, whole grains, nuts and legumes, and limits saturated fat, cholesterol, red and processed meats, added sugars, and sugar-sweetened beverages. It was originally developed in the US to treat hypertension without medication [5]. Several medical associations and institutions have since incorporated the diet in their clinical guidelines [6]. 

REFERENCES:

[1] Ritchie & Roser (2019). Meat and Seafood Production & Consumption. Published online at OurWorldInData.org. Retrieved from: https://ourworldindata.org/meat-and-seafood-production-consumption on 28 August 2019

[2] Dinu, Pagliai, Casini & Sofi (2018). Mediterranean diet and multiple health outcomes: an umbrella review of observational studies and randomised trials. European Journal of Clinical Nutrition, 72(1), 30-43. doi: 10.1038/ejcn.2017.58

[3] Cordain, Eaton, Sebastian, Mann, Lindeberg, Watkins et al. (2005). Origins and evolution of the Western diet: health implications for the 21st century. American Journal of Clinical Nutrition, 81(2), 341-354. doi: 10.1093/ajcn.81.2.341

[4] US Department of Agriculture, Food and Nutrition Service. Retrieved from https://www.fns.usda.gov/resource/healthy-eating-index-hei on 28 August 2019

[5] Sacks, Svetkey, Vollmer, Appel, Bray, Harsha et al. (2001). Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. DASH-Sodium Collaborative Research Group. The New England Journal of Medicine, 344(1), 3-10. doi: 10.1056/NEJM200101043440101

[6] Chiavaroli, Viguiliouk, Nishi, Mejia, Rahelic, Kahleova et al. (2019). DASH Dietary pattern and cardiometabolic outcomes: an umbrella review of systematic reviews and meta-analyses. Nutrients, 11(2), 338. doi: 10.3390/nu11020338

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Why do we eat what we eat? What makes us choose an apple over chocolate cake, or the other way around? How do we decide whether or not to have that tempting dessert, despite feeling satiated after a hearty meal? I previously wrote about how our daily food choices are, at least in part, influenced by our genetic make-up, but there are many other factors determining what, when, where and why we eat. Today I will discuss the importance of personality traits.

Personality is a set of relatively stable traits, that together determine who we are. While some characteristics of us change day by day, or even hour by hour, others are more stable. For instance, although we all feel worried from time to time, you may – generally speaking – be easily worried or nervous. The famous Big Five model of personality proposes that all people can be described in terms of five traits: neuroticism, agreeableness, openness to experience, conscientiousness and extraversion. These five traits in turn host a number of more specific characteristics, such as impulsivity, self-consciousness, anger, excitement seeking and thoughtfulness.1

What does this have to do with eating habits? Well, as it turns out, specific personality traits are associated with different food choices. Most studies look at healthy versus unhealthy food choices. A healthy diet has consistently been associated with the Big Five trait “conscientiousness”, which includes characteristics such as self-discipline, diligence, thoughtfulness and goal-orientedness. An unhealthy diet, on the other hand, has been associated with neuroticism, stress-sensitivity and impulsivity.2 Impulsivity and neuroticism have also been linked to emotional eating, binge-eating, external eating and (not surprisingly) stress-eating and impulsive eating (e.g. 3).

So, among the numerous factors influencing what, when, where and why we eat, how important are personality traits? Imagine a test in which we ask participants to choose between an apple and chocolate cake. Indeed, knowing how impulsive, neurotic and conscientious these participants are helps us better predict what they’ll choose; however, the accuracy of our prediction would improve only very slightly compared to a prediction without knowing the participants’ personality. In my own study (which is ongoing and therefore yet unpublished), I found that those with an extremely high score on an impulsivity questionnaire (i.e. higher than 97% of all other participants), on average, consumed 2192 kcal per day, compared to an average of 2030 kcal/day for those with an extremely low impulsivity score (i.e. those scoring lower than 97% of all other participants). For self-discipline, a trait belonging to the conscientiousness domain, the effect was even smaller: extremely self-disciplined people on average consumed only 112 kcal per day less compared to people with an extreme lack of self-discipline. To give you an indication, 112 kcal equals about one medium-sized cookie, or one glass of orange juice. In other words, being a conscientious person doesn’t mean one will always choose the healthy option over the unhealthy one; nor will impulsive or neurotic people always choose chocolate over apples.

Mind you, the above reported findings are associations. Although it is compelling to think that impulsivity causes us to make unhealthy food choices, it may in fact be the other way around! Perhaps an unhealthy lifestyle makes us more impulsive. We do know, for instance, that certain mental health conditions can be improved by healthier diets, suggesting that what we eat can change the way we feel and behave (rather than the other way around). This question of “direction of causality” is an important and very challenging issue that we, researchers, urgently need to tackle.

Finally, a few words on attention-deficit hyperactivity disorder (ADHD); after all, impulsivity is one of its key symptoms. Does this mean that people with ADHD make less healthy food choices? Indeed, this seems to be the case. Studies have shown that – on average – people with ADHD have less healthy eating habits4, and are more prone to overweight and obesity5,6, compared to people without ADHD. However, other factors associated with ADHD may contribute to poorer eating habits as well. For instance, lower socio-economic status makes healthier foods less accessible to people with ADHD, as healthier foods are generally more expensive; also, lower levels of education may result in people with ADHD knowing less about healthy and unhealthy lifestyles.

REFERENCES

  1. Costa, P.T., McCrae, R.R. (1992). Revised NEO Personality Inventory (NEO-PI-R) and NEO Five-Factor Inventory (NEO-FFI) manual. Odessa, FL: Psychological Assessment Resources
  2. Stevenson (2017). Psychological correlates of habitual diet in healthy adults. Psychological Bulletin, 143(1), 53-90
  3. Keller, C. & Siegrist, M. (2015). Does personality influence eating styles and food choices? Direct and indirect effects. Appetite, 84, 128-38
  4. Ríos-Hernández, A., Alda, J.A., Farran-Codina, A., Ferreira-García, E., Izquierdo-Pulido, M. (2017). The Mediterranean Diet and ADHD in Children and Adolescents. Pediatrics, 139(2)
  5. Bowling, A.B., Tiemeier, H.W., Jaddoe, V.W.V., Barker, E.D., Jansen, P.W. (2018). ADHD symptoms and body composition changes in childhood: a longitudinal study evaluating directionality of associations. Pediatric Obesity, 13(9):567-575
  6. Chen, Q., Hartman, C.A., Kuja-Halkola, R., Faraone, S.V., Almqvist, C., Larsson, H. (2018). Attention-deficit/hyperactivity disorder and clinically diagnosed obesity in adolescence and young adulthood: a register-based study in Sweden. Psychological Medicine, 1-9 (e-pub)
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We, human beings in Western society, make over 200 food choices each day (1). That’s a lot! Fortunately (or, according to others, unfortunately), we don’t actually have to think about each and every one of them, or at least not consciously. If our food choices are not so much a conscious decision, then how do we make them? A lot has been written about external factors influencing our food choices, for instance, alluring displays in supermarkets or the availability of unhealthy foods in our day-by-day environment. In this blog, I will address the potential role of genetics on food choices: to what extent do our genes determine what we eat?

Eating behaviours are complex, i.e. they are very diverse and influenced by many different factors. When we investigate complex behaviours, we are unlikely to find simple explanations. In other words: we do not expect to find one gene that makes me prefer pizza margarita over pizza fungi, nor will we find a single gene responsible for my triple-chocolate ice cream consumption. There are, however, some instances in which specific genes have relatively simple and straightforward effects on our food choices. This is the case when genetic variants code for food sensitivities.

A famous example is the LCT gene (or, more precisely, the C>T change at 13910 bases upstream of the LCT gene in the 13th intron of the MCM6 gene). The LCT gene codes for lactase persistence, or lactose tolerance after childhood. Worldwide, the majority of people (and most other mammals, for that matter) no longer tolerate dairy products after childhood. For them, consuming milk products causes nausea, bloating and cramping within 2-3 hours. As a result, they will soon learn not to consume dairy products. Those who have the lactase persistence gene, however, don’t have any problems digesting dairy products and, thus, are more likely to consume them (2). Geographical region is important here: while in Northern European countries such as the UK and Finland, 90-100% of people tolerate dairy products, in South-East Asia and Australia this number is close to 0% (3).

A similar situation seems to occur for genes coding for certain taste receptors on the tongue. The TAS2R38 gene, for instance, makes some people extremely sensitive to bitter taste. This, of course, will cause them to avoid bitter foods such as cruciferous vegetables (4). A recent study has even identified a small number of genes that together cause people to either love or hate marmite (5)! Another gene variant (CYP1A1), coding for caffeine clearance from the body, causes carriers to drink less or more coffee and tea (6).

Thus, when food sensitivities are involved, food choices can be driven by specific genes. Most food choices, however, have very little to do with food sensitivities and are much more complex. Pizza Margarita or Pizza Funghi? Triple-chocolate ice cream today or maybe tomorrow? While for such complex food choices there is no single gene responsible, our genetic make-up still does have influence. Typically, for complex behaviours, many different genes can be identified. While each gene individually contributes only a little bit, together they can actually have quite an effect on your food choices. For instance, a recent study identified seven genetic variants each having a small effect on carbohydrate intake. Taken together, genes explained 8% of the variation in carbohydrate intake between individuals (7).

In conclusion: while some genetic variants have rather drastic effects on our food choices, by giving us a physical adverse reaction to certain foods, there are only few of them. Most of our food choices are much more complex. These are influenced by multiple genes at the same time, and even together these genes have only limited influence.

REFERENCES
1. Wansink, B., & Sobal, J. (2007). Mindless eating: The 200 daily food decisions we overlook. Environment and Behavior, 39(1), 106-123. doi: 10.1177/0013916506295573

2. Szilagyi, A. (2015). Adaptation to Lactose in Lactase Non Persistent People: Effects on Intolerance and the Relationship between Dairy Food Consumption and Evolution of Diseases. Nutrients, 7(8):6751-79. doi: 10.3390/nu7085309

3. Itan, Y., Jones, B.L., Ingram, C.J.E., Swallow, D.M. & Thomas, M.G. (2010). A worldwide correlation of lactase persistence phenotype and genotypes. BMC Evol Biol, 10:36. doi: 10.1186/1471-2148-10-36

4. Feeney, E., O’Brien, S., Scannell, A., Markey, A. & Gibney, E.R. (2011). Genetic variation in taste perception: does it have a role in healthy eating? Proc Nutr Soc, 70(1):135-43. doi: 10.1017/S0029665110003976.

5. Roos, T.R., Kulemin, N.A., Ahmetov, I.I., Lasarow, A. & Grimaldi, K. (2017). Genome-Wide Association Studies Identify 15 Genetic Markers Associated with Marmite Taste Preference. BioRxiv (preprint). doi: 10.1101/185629

6. Josse, A.R., Da Costa, L.A., Campos, H. & El-Sohemy, A. (2012). Associations between polymorphisms in the AHR and CYP1A1-CYP1A2 gene regions and habitual caffeine consumption. Am J Clin Nutr, 96(3):665-71. doi: 10.3945/ajcn.112.038794.

7. Meddens, S.F.W., de Vlaming, R., Bowers, P., Burik, C.A.P., Karlsson Linnér, R., Lee, C., et al. (2018). Genomic analysis of diet composition finds novel loci and associations with health and lifestyle. BioRxiv (preprint). doi: 10.1101/383406

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Loss of appetite is among the most common side effects of stimulant for ADHD. Across studies, approximately 20% of patients with ADHD who were treated with stimulants reported a loss of appetite [1,2]. Weight loss is also quite common, as are digestive problems [3]. Together, such side effects are often referred to as “gastro-intestinal adverse events”. But why do stimulants change the way we go about eating? And what could this tell us about ADHD itself?

Appetite can arise in response to physical cues, such as an empty stomach or low blood sugar. Psychological cues can also influence our appetite; for instance, we may get hungry when we watch other people eat, or when we are bored. For most people, eating is a pleasant and rewarding activity. In the human brain, pleasure, reward, craving and, thus, appetite, have everything to do with dopamine. More specifically, with dopamine levels in the striatum, a cluster of neurons at the very base of the forebrain. The striatum is strongly connected with the prefrontal cortex. The prefrontal cortex exercises cognitive control over the urges of the striatum: when we’re hungry, the striatum makes us crave high-caloric, high-fat, or sweet foods; at the same time, our more rational prefrontal cortex helps us make responsible food choices.

Interestingly, ADHD also has everything to do with dopamine and the striatum. Dopamine levels in the striatum are slightly ‘off’ in individuals with ADHD. As a result, people with ADHD feel a higher urge to seek pleasant experiences, and less prefrontal control over this urge. Impulsivity, a prominent feature of ADHD, can be viewed as a failure to sufficiently activate the prefrontal cortex. Finding a balance between pleasure-seeking on the one hand, and rational decision-making on the other, can be difficult for all of us. However, for people with ADHD whose dopamine balance is slightly off, making healthy, non-impulsive decisions about what to eat may be even more challenging. Indeed, overweight, obesity and diabetes seem to be more common in people with ADHD compared to people without ADHD [4].

Stimulants such as methylphenidate and dexamphetamine can restore the dopamine balance in the brain. This may result in less craving for food (as well as for other pleasant activities) and more control over impulsive urges. It is thus not very surprising that stimulant medications may cause a loss of appetite or even weight loss. Interestingly, stimulants are sometimes used to treat obesity and certain eating disorders as well. Especially for eating disorders involving impulsive eating, such as bulimia nervosa and binge-eating disorder, stimulant treatment could be promising. [5]

There is one other interesting angle on stimulants, dopamine, and eating. Did you know that most of the dopamine in your body is not located in the brain? In fact, a substantial proportion of all dopamine-related processes in the human body take place in the gut. Throughout the gastro-intestinal tract, dopamine receptors are abundant. Therefore, in addition to the indirect effects described above (i.e., via craving and/or impulse control), stimulants may have direct effects on eating behaviours as well. Unfortunately, we know very little about such direct effects.

REFERENCES
[1] Storebø, Ramstad, Krogh, Nilausen, Skoog, Holmskov et al. (2015). Methylphenidate for attention-deficit/hyperactivity disorder in children and adolescents: Cochrane systematic review with meta-analyses and trial sequential analyses of randomised clinical trials. Cochrane Database Syst Rev (11):CD009885. doi: 10.1002/14651858.CD009885.pub2

[2] Storebø, Pedersen, Ramstad, Kielsholm, Nielsen, Krogh et al. (2018) Methylphenidate for attention deficit hyperactivity disorder (ADHD) in children and adolescents – assessment of adverse events in non-randomised studies. Cochrane Database Syst Rev 5:CD012069. doi: 10.1002/14651858.CD012069.pub2

[3] Holmskov, Storebø, Moreira-Maia, Ramstad, Magnusson, Krogh et al. (2017) Gastrointestinal adverse events during methylphenidate treatment of children and adolescents with attention deficit hyperactivity disorder: A systematic review with meta-analysis and Trial Sequential Analysis of randomised clinical trials. PLoS One 12(6):e0178187. doi: 10.1371/journal.pone.0178187

[4] Cortese, Moreira-Maia, St Fleur, Morcillo-Peñalver, Rohde & Faraone (2016). Association Between ADHD and Obesity: A Systematic Review and Meta-Analysis. Am J Psychiatry 173(1):34-43. doi: 10.1176/appi.ajp.2015.15020266

[5] Himmerich & Treasure (2018). Psychopharmacological advances in eating disorders. Expert Rev Clin Pharmacol, 11(1):95-108. doi: 10.1080/17512433.2018.1383895

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