By Dr Christian Thoma

Have you ever wondered how different ‘experts’ in nutrition can have such differing opinions, or why the news headlines seem to constantly go from saying something is bad one week to saying the same thing is good the next? Some of this is sensationalist, or even just plain bad reporting. Some of it is human nature. But some of it is because far from being simple, the science of nutrition is pretty complicated.

Healthy eating doesn’t have to be hugely complex, at least not for most of us, but nutrition as a science is far from straightforward. For example, there are three main macronutrients that provide energy and building blocks for our body: protein; fat (including oils); and carbohydrates. Add to that alcohol, which isn’t really a nutrient, but provides more calories per gram than protein or carbohydrates, and dietary fibre, which, among other things, provides some energy indirectly via the bacteria living in our bowels. For most people, only two of these are essential to life: proteins and fats/oils. 

Carbohydrates are mostly made up of the units: glucose; fructose; and galactose. These units combine in different ways, e.g. sucrose or table sugar made up of one glucose unit and one fructose unit, lactose or milk sugar is made up of one galactose unit and one glucose unit, and starch is made up of very long strings of glucose units.  All of the variations have subtly and sometimes not so subtly differing effects on our bodies (1). For example, glucose has a big effect on how much insulin our bodies produce and need (2), whereas fructose has little to no immediate effect (3). Insulin being a hormone that helps control blood glucose and regulate how we use or store fat (4). The carbohydrates in some foods and meals are rapidly digested and absorbed, and can cause a spike in blood glucose (5). High average concentrations of glucose in the blood are the hallmark of type 2 diabetes. Whereas excess dips in blood glucose can make it hard to concentrate (6).  

Proteins are made of amino acids of which there are 20/21, 8 of which are essential, but some are conditionally essential – essential in certain circumstances (7). The specific amino acids in the proteins we eat have specific effects on our bodies, for example  the amino acid leucine causes an increase in blood insulin (8,9), and typtophan is the base on which our bodies produce the neurotransmitters serotonin and melatonin, which affects our mood, mental function, and sleep (10,11). Not all food proteins are made up of the same amino acids or in the same proportions (12). The type of protein can make a difference to our appetite and health (12-16). Making claims about ‘high’ or ‘low’ protein diets without considering some of the specifics of those proteins is missing a potentially important part of the nutrition puzzle, yet this is almost always what reports about nutrition do.

Fats can be divided into saturated, monounsaturated, polyunsaturated, and trans-fats. The last can be further divided into conjugated and non-conjugated. Polyunsaturated fats are divided on the basis of specifically where they have the double-bonds that make them ‘unsaturated’; hence we get omega-3, omega-6, and omega-9 varieties. Fats also consist of different fatty acids and can come as triacylglycerols, diacylglycerols, mono-acylglycerols, non-esterified fatty acids, cholesterol esters, phospholipids, and a few other varieties. Fatty acids can be short, medium, long and very long chain. And it goes on. These aren’t trivial distinctions either as they have effects on everything from digestion to influencing inflammation (17,18), and many aspects of health in-between (19,20). For example, nutritionists have been aware for some time that the effect of saturated fat on cholesterol depends on the specific length of that fat (21). Defining a diet purely on the totality of fat, or even just dividing the types of fat into broad categories, misses the importance of ratios and specifics.

Another problem with comparing dietary approaches in studies is that, at least when it comes to the macronutrients (that’s fats/oils, proteins, and carbohydrates) we can’t isolate a single quantity. If you reduce carbohydrates you either reduce total energy (calories), or you have to replace the carbohydrate with fat, protein, or both to make up the energy difference. It’s impossible to just make one change. This has caused no end of problems when it comes to labelling diets in studies. 

There are no clearly defined universally excepted dietary labels. You’ll read headlines like High fat diet increases risk of heart disease and High fat low carbohydrate diet reduces heart disease risk factors, and you’ll either be cynical and just keep doing what you’re doing because ‘these scientists can’t make up their minds’, or you’ll ask yourself ‘what is going on here?’ Chances are the two diets in these studies were quite different. The study showing a high fat diet was linked with higher risk of heart disease probably looked at diets where 35-50% of the calories came from fats, whereas the second study probably looked at a diet where 70-80% of calories were coming from fat and only 10% or so from carbohydrates. Both studies are higher in fat than common recommendations, but one brings about a very different shift in physiology and therefore risk of disease than the other.

Another way in which diets vary, beyond ratios and specifics is how much energy (calories) they provide. Diets can provide just enough to meet a person’s needs, provide less (for weight loss), or provide more (for weight gain). The body responds quite differently to getting too much than it does to getting too little. For example, weight reduction is often accompanied by cholesterol reduction irrespective of diet, but when the weight reduction stops, the cholesterol may well go back up on that same diet (22).

Not only does what and how much we eat make a difference, but when and how frequently we eat does (23-30). Even if the carbohydrate, protein, and fat ratios as well as energy (calories) are kept the same overall, how these are distributed across the day, e.g. big breakfast/small dinner vs. small breakfast/big dinner (31), or carbohydrates mostly in the evening vs. throughout the day (32), can make a noticeable difference to our bodies in terms of weight and health. So what we consume, and when is going to make a noticeable difference.

This all assumes that the people in the study did exactly what they were told, or reported exactly what they did, and that the methods used to measure the outcomes of interest were the same, or at least readily comparable. In reality, some of us are really strict when we do something and will carefully weigh out and consider every morsel. Others are of the view that ‘near enough is good enough’, and so may be out by quite a bit. Also, some studies ask people to live on a hospital ward where they can be observed and provided specific food at specific times, while others might just provide some recipe ideas and basic instructions. These different circumstances will have an affect on adherence, outcomes, and therefore conclusions.

Another difference that won’t usually make it into a news report and that you would need specialised knowledge to spot, is use of different methods in different studies. For example, one of the most commonly reported outcomes in nutrition studies is LDL-cholesterol. This is also commonly done in standard medical checks. The thing is the LDL-cholesterol is rarely measured, instead it’s estimated based on other things that are measured, so the accuracy may not always be that good (33-35). In addition, LDL-cholesterol and HDL-cholesterol come in different forms, with some more harmful or beneficial than others (36,37). So a study reporting no change, or a potentially adverse change, in estimated total LDL-cholesterol may be masking the fact that there was a shift in the type of LDL-cholesterol. Research costs a lot of money, and yet is poorly funded, so researchers often have to go with the cheaper and/or easier option. 

If you’re confused by all this, then you get the point. All this complexity is confusing. Although much is known about nutrition, there is a lot that isn’t known. The day-to-day practice of nutrition is therefore as much an art as a science, and much of the information in popular books and throughout the internet is opinion. The best results in terms of health come to those willing to learn with great coaches combined with some self-experimentation.

For more insight into the how even similar looking diets can differ in important ways, and how that affects the results of nutrition studies, please read Part 2 and Part 3. Also check out the EAT101 series to build your understanding of nutrition from the basics up. 

References: click here to see the full list of references cited.

Nutrition Consultations: want coaching on your journey to better health and greater happiness? Check out our Nutrition or Comprehensive Health Coaching services or organise a seminar for your work, group, or team.

By Dr Christian Thoma

Part 1 introduced the uncertainty in nutrition research arising from the many forms and affects of different macronutrients, namely fats, proteins, and carbohydrates. If you haven’t already, reading part 1 will clarify what this series is all about. As you read, bare in mind that healthy eating doesn’t have to be complex, at least not for most of us, but that this series is about showing why, as an area of study, nutrition is far from straightforward.

The macronutrients discussed in part 1 only cover some of our nutrition needs. To survive we also need adequate amounts of the micronutrients – vitamins and minerals, including those some call trace elements (1). These don’t provide fuel directly, but they are essential for literally thousands of life-sustaining functions in the body, including our ability to use the macronutrients properly and efficiently. 

The recognised vitamins are: A (retinol, retinal, retinoic acid); B1 (thiamine); B2 (riboflavin); B3 (niacin/niacinamide); B5 (pantothenic acid); B6 (pyridoxine, pyridoxal, pyridoxamine); B7 (biotin); B9 (folate); B12 (cobalamins); C (ascorbic acid/ascorbate); D (cholecalciferol, ergocalciferol); E (tocopherols, tocotrienols); K (phylloquinones, menaquinones) (1). The recognised minerals are: calcium; chlorine; copper; iron; magnesium, manganese, molybdenum, potassium; selenium; sodium; and zinc (1). From time-to-time, other food components are proposed for addition to what is recognised as essential, and we may yet discover that some of them are.

Some vitamins come in different forms and the effects and potency of those different forms are not all equal. Some food components, notably the carotenoids, are not strictly speaking vitamins, but our bodies can convert beta-carotene into a vitamin A for example (1). Minerals in also come in different forms, such as being bound to proteins, e.g. iron bound to haemoglobin, although this doesn’t so much affect their activity or potency once absorbed into our body, it does affect how readily absorbed they are; or in the scientific jargon (2,3), how bioavailable they are.

You could be forgiven for believing that nutrient deficiencies are restricted to economically poorer countries or people with very restrictive diets, but this isn’t the case. Although life threatening nutrient deficiencies are rare in economically developed countries, many people are likely not to be getting optimal amounts (4-8). For example, many countries, including New Zealand, the UK, the USA, Spain, and Australia have areas or sections of the population with mild-to-moderately iodine deficiency (9,10). Rickets, caused by vitamin D deficiency is making a comeback in the UK (11), and less severe deficiency may be affecting the majority of European adults (4). Some groups are at greater risk than others. Premenopausal women are at risk of iron deficiency (1), and financially poorer minority groups are at higher risk for multiple deficiencies etc (7,12).

In addition to many people just getting less than the recommended amounts of vitamins and minerals in the diet, some things increase our need for certain vitamins and or minerals. As a rule, national and international guidelines for getting enough vitamins and minerals specifically state that they are for healthy people. The problem is that research is seldom done in truly healthy people. Research is done in a mix of people, or in people who have one or more illnesses, or at least things considered to represent a high risk of poorer health, e.g. obesity. Some people will need more of certain vitamins and minerals than is considered necessary to maintain health in the healthy, e.g. having to deal with pollutants in the air, food, and water can also change the amount of vitamins and minerals we need (13), as can being obese (14-18).

Despite some level of measurable nutrient deficiency being likely to affect many participants in nutrition research, the presence or absence of nutrient deficiencies are rarely assessed. Diets used in research are often more well thought out than what the study volunteers normally eat, so they are likely to provide more vitamins and minerals and thereby reduce nutrient deficiencies. Also, because vitamins and minerals are involved in the metabolism of the macronutrients (fats, proteins, and carbohydrates), changing the ratio of macronutrients would change the amount of vitamins and minerals an individual needs to be optimally healthy. Study diets may well affect not only how much of each vitamin and mineral volunteers are getting, but also how much they need for health. Some of the improvements in health observed in these studies may well be due to the unintended reduction of nutrient deficiencies, and not what the authors of the studies measure and report. Until this is directly assessed, we won’t know to what extent this is true.

Unless you eat offal consistently, especially liver and kidney, you probably get the bulk of your vitamins from vegetables and fruit. Plant foods have another key component, namely dietary fibre. Not very easy to define (19), dietary fibre is basically the food components we can’t digest. Although they aren’t absorbed, dietary fibres can affect things such as appetite (20), how much cholesterol we reabsorb (21), and how quickly what we eat travels through our bowels (22-24). Some dietary fibres are a source of food for the bacteria that call our bowels home (25-27); when isolated and sold as supplements or food additives these fibres are often called prebiotics (more on that in part 3). Dietary fibres affect health, sometimes for the better and sometimes for the worse. It would be easy to design a diet identically high or low in fats, proteins, and carbohydrates, but very different in terms of the types and amounts dietary fibres. This is another example of how changing one thing, results in changing many.

In summary, when researchers focus mainly on how much of each macronutrient their study volunteers are getting, they will miss the contribution and distribution of vitamins, minerals, and fibre. Even the more holistically minded will struggle to find out what the exact composition of volunteer diets is as this would require a duplicate of those diets to be analysed for all the potential components of interest. That would be a very expensive option.

So far we’ve mostly focused on how diets that look similar when reduced to a few numbers can be very different when looked at more holistically. That’s still only one side of the coin when it comes to understanding the challenge faced by professional and amateur nutrition researchers, part three will look at how the person eating the diet in question influences the outcomes. If you want to know how genes, disease, our microbial ecosystem, and our allergies and intolerances add another layer of complexity to the nutrition research, read part 3 of this series.

Check out the EAT101 series to build your more formal understanding of nutrition from the basics up. Additionally, or alternatively read about our health coaching service that guides you to finding what is right for you across all our five themes: Think, Move, Breathe, Eat, Recover.

References: click here to see the full list of references cited.

Nutrition Consultations: want coaching on your journey to better health and greater happiness? Check out our Nutrition or Comprehensive Health Coaching services or organise a seminar for your work, group, or team.

By Dr Christian Thoma

Parts 1 and 2 of this series introduced the idea that diets that look the same at first glance, can be very different once we look a little closer. Part 2 also introduced the idea that some people in a given study may start out having some degree of vitamin and/or mineral deficiency, which a well designed experimental diet may fix. In this concluding part we’ll continue the idea that what gets eaten is only part of the story, the other part being who is doing the eating. What is good for one person, or at least good enough, won’t be for another.

Except for ‘identical’ twins triplets etc., we each have a unique set of genes. Even in identical twins those genes will be expressed in a unique way. Our genes are our blueprint, and determine a lot about us. Consider that your body is full of all kinds of cells: white blood cells; liver cells; bone cells; nerve cells etc. Each of these contain the same genes that provide the blueprint for all the other cells, but how that blueprint is and isn’t expressed, which ones are switched on and which off, determines whether a cell is a liver cell, a nerve cell, or another kind of cell. Why is this relevant? Because what we eat affects our genes (this is studied by the field of nutrigenetics), and our genes help determine how we interact with what’s in our food (this is studied by the field of nutrigenomics) (1,2).

Some of us may benefit from something while others don’t, or are even harmed by it. When there are strong genetic differences in different people break down a component of food, this can lead to some very conflicting research when those differences aren’t considered. Research into the health benefits, or lack of them, due to caffeine is a good example (3,4). Some of us breakdown caffeine faster than others; the health consequences eating and drinking caffeine rich foods such as coffee, tea, and high cocoa chocolate therefore vary from person-to-person. We also differ in how well our bodies cope with alcohol (5), respond to different fats (6), and deal with various types of medication (7-9). However, to date, few studies have looked at volunteers’ genes to see how much they might be influencing findings.

Genes aside, studies are often done in people with specific medical conditions that are related to, or can at least be improved with diet, e.g. thyroid conditions, metabolic syndrome, different types of diabetes, and bowel conditions. These all influence how the body deals with the macronutrients (fats, proteins, and carbohydrates). They are often either studied in isolation, or the focus is on one condition and the others are mostly ignored. In reality, it is common for people to have more than one major medical condition. 

In addition to our genes, common and not so common medical conditions such as hypo-/hyperthyroidism, metabolic syndrome, diabetes, inflammatory bowel disease, coeliacs disease etc. all profoundly affect how our bodies react to the food we eat. The effect of different diets in these conditions are relatively well studied individually, but many people will have more than one, e.g. a thyroid condition and type 2 diabetes. Such a person may well respond differently to the same diet as someone with just hypothyroidism or just type 2 diabetes. The lesson here is that even though people in one study at first glance appear very similar to people in another study, they may not be. Such unreported differences in volunteers are just as important as unreported differences in diets.

Before the food we eat even has a chance to interact with our genes, or our medical condtions, it first comes into contact with the bacteria that call our bowels home. It’s estimated that for every human cell we have about 10 bacterial cells living in or on us. A large portion of these bacteria live in our colon, but many also live in the small intestine where most food is digested and absorbed (10). Research is showing us that this is a complex ecosystem that changes rapidly with what, when, and possibly how much we eat,(11-16). Additionally, our own physical characteristics affects the types and proportions of bacteria calling each of us home (17). This is no simple relationship and is very much a two way street in which our bodies communicate with these microbes and they with us (18,19). The bacteria in our bowels help us digest food (20), and breakdown toxins and medicines (21). Some of the bacteria can actually produce the same hormones and neurotransmitters – chemical signals – that we do (19). A healthy gut ecosystem also makes it harder for illness causing bacteria and yeasts to get a foothold and cause us problems (10). 

Some of the latest research shows that being obese and/or having metabolic syndrome, type 2 diabetes etc. can also mean having more bacteria particularly good at helping us get every last bit of energy from the food they eat (22-25), and that lifestyle changes commonly recommended to improve health may in part be beneficial because they change what’s living inside us (26). Although scientist now have tools to look at our bacterial selves, we aren’t that clear on what to make of the results (27), but there is a good chance that our individual ecosystems help determine what dietary approach is most successful for each of us (28).

Beyond genes, our own and those of our microbial ecosystem, and in addition to any common illnesses we may have, there are food preferences, intolerances/hypersensitivities, and allergies. We know our preferences, but may be unaware of  allergies or intolerances that affect us because sometimes the symptoms aren’t felt in our bowels and/or aren’t felt until hours or even days after we’ve eaten the problem food (29). The same foods that provide a rich source of vitamins, minerals, and/or non-essential but health promoting nutrients to one person, can be a double-edged sword to another who has an underlying sensitivity to that food or group of foods (30). A given dietary approach may, unintentionally, increase of decrease the amount of the problem food without anyone being the wiser that this influenced the results.

Yet another factor influencing how we interact with what we eat is our recent physical activity or lack thereof, as well as the quality and quantity of sleep we’ve had. For example, exercise generally makes us better at dealing with both carbohydrates and fat (31,32). How much of an effect depends on many factors such as the intensity, duration, and timing of the exercise. The same diet in a group of people who are frequently active shortly before or shortly after a meal, will have a different affect than a diet in people who are mostly sedentary. Similarly, any sort of sleep deprivation can change how well our body deals with what we eat, and even our appetite and food choices (33,34). Regular good sleep is associated with greater success when trying to reduce weight (35-37). In science, as in the rest of life, we are unlikely to get answers to questions we don’t ask.

In summary, one size does not fit all no matter how good the marketing spin is. Diets vary hugely in their specific makeup even when they look similar when summarised. They may vary in terms of the macronutrients (fats, proteins, and carbohydrates) and/or in terms of the micronutrients (vitamins and minerals), other nutrients that are not essential to life but influence our health, and the degree to which they trigger any allergies or intolerances. We in turn are just as varied in terms of our genetic makeup, medical conditions, the microbial ecosystems that call our bodies home, personal preferences, recent physical activity, and sleep quality and quantity. How all these things interact will ultimately decide how healthy/effective a diet is for any given individual at any given time.

Given all this possible complexity it's no wonder everyone wanting to make broad statements, develop population guidelines, or sell books on the one solution will fight tooth and nail to try and convince you that they have it right. Science doesn't have all the answers, that's why each year more research is done, not less. Everyone needs enough of the essentials and not too much, but what that means in real practical terms will vary tremendously from person to person. There is no single solution or guideline, nor can there be, that will promote health in everyone. There is however a single approach – that of self-discovery and guided, or at least informed, self-experimentation. If you want to thrive, learn what works for you:

1. Clean your slate; everyone, even ‘experts’, has a lot more to learn about nutrition.
2. Build a good grounding of basic knowledge, or seek out someone with a solid base of theory as well as a scientific mindset.
3. With guidance or on your own, start making small changes to your diet and carefully track your response to find what works best for you. Patience is a virtue as it could take days, weeks, or months to see a big change; it depends on what change you’re looking for. Some things will make a big difference quickly.

Check out the EAT101 series to build your understanding of nutrition from the basics up. Additionally, or alternatively, read about our health coaching service that guides you to finding what is right for you across all our five themes: Think; Move, Breathe, Eat, Recover.

References: click here to see the full list of references cited.

Nutrition Consultations: want coaching on your journey to better health and greater happiness? Check out our Nutrition or Comprehensive Health Coaching services or organise a seminar for your work, group, or team.