Why Nutrition Studies Keep Contradicting Each Other

Summary

This SciShow episode explores the confusion surrounding nutrition research, highlighting the challenges in interpreting studies on food and supplements. It discusses conflicting findings, such as the effects of red wine and raspberries on health, and the complexities of translating animal research to humans. The video emphasizes that individual studies often contribute to a larger puzzle, and their outcomes should be taken with caution. The key takeaway is the importance of understanding the specific contexts and details of nutrition studies, rather than seeking broad, definitive answers about what is 'good for you.'

Takeaways

• 🍷 The perception of whether red wine is good for you is inconsistent due to varying study results and headlines.
• 🍇 A 2011 Chinese study found red raspberries could improve blood pressure, while a 2013 Finnish study found fresh berries had no effect, highlighting the complexity of nutrition research.
• 🐁 The differences in study design, such as using animal models versus human subjects, can lead to contrasting outcomes.
• 🧪 Nutrition research often involves imperfect comparisons, making it difficult to translate results into practical advice.
• 🍓 The effects of a single compound may differ from the effects of the entire food, as observed in the raspberry studies.
• 🔍 Examining studies more closely can help to untangle the confusion caused by seemingly contradictory findings.
• 🍇 The type of study (e.g., randomized controlled trials vs. observational studies) and the specific conditions under which they are conducted are crucial for understanding results.
• 🥤 Beta carotene, found in foods like carrots, was thought to lower lung cancer risk, but high doses in supplements had the opposite effect in smokers.
• 🧬 Nutrition studies are part of a larger research puzzle and are not always meant to be taken as direct advice for consumers.
• 🍷 Resveratrol in red wine, an antioxidant, showed positive cardiovascular effects in a 2012 study, but a 2014 study found no such effect, illustrating the variability in study outcomes.
• 🥤 The definition of 'good for you' is not universally agreed upon and can vary widely depending on the specific health outcomes being studied.

Q & A

Why is it difficult to get a definitive answer on whether a certain food or supplement is beneficial for health?

It's challenging because nutrition research often produces conflicting results due to factors like different study designs, subjects (animals vs. humans), and the complexity of isolating the effects of individual compounds within foods.

What was the contradiction found in the studies about red raspberries and blood pressure?

A 2011 Chinese study using raspberry extract on rats found it could improve blood pressure, while a 2013 Finnish study using berry puree on humans with increased heart disease risk found no effect, highlighting the differences in study methods and subjects.

Why might the results from animal studies differ from those in humans?

Animal studies allow for more control over variables like diet and exercise, but humans have more complex lifestyles and may be influenced by factors that can't be controlled in a lab setting, which can affect the outcome of nutritional studies.

What is a Randomized Controlled Trial (RCT) and why is it significant in human studies?

An RCT is a type of study where participants are randomly assigned to either an experimental or control group to minimize bias. It is significant because it is considered the closest to a controlled experiment in humans without ethical violations, aiming to isolate the effect of a specific intervention.

How does an observational study differ from a Randomized Controlled Trial?

Observational studies gather existing data, such as through interviews or analyzing biological samples, without manipulating the subjects' conditions. They differ from RCTs, which involve assigning participants to groups and introducing specific interventions to observe their effects.

What was the contradiction found in the studies regarding resveratrol in red wine and cardiovascular health?

A 2012 RCT found that resveratrol supplements improved cardiovascular health indicators in adults, while a 2014 observational study in Italy found no effect of resveratrol on cardiovascular disease or mortality, suggesting that the form and dosage of resveratrol may impact its effectiveness.

Why did beta carotene supplements have a different effect compared to the natural form found in foods?

Observational studies showed that a diet rich in beta carotene lowered lung cancer risk, but clinical trials found that high doses of beta carotene supplements increased lung cancer rates in smokers, indicating that the form and dosage of a nutrient can significantly affect health outcomes.

What is the importance of understanding the specific health outcomes, or 'outcomes', in nutrition studies?

Understanding specific outcomes is crucial because they provide clarity on what aspect of health a study is examining, such as rates of certain diseases or levels of specific biomarkers, rather than making broad generalizations about a food or supplement being 'good' or 'bad'.

How does alcohol present a complex picture in nutrition research?

Alcohol has been associated with both positive and negative health effects. Light to moderate drinking may have cardiovascular benefits, but excessive consumption can lead to liver damage, increased cancer risk, and other health issues, illustrating the nuanced relationship between diet and health.

Why is it recommended to view individual nutrition studies with caution?

Individual studies should be viewed with caution because they often represent a piece of a larger puzzle and may not account for all variables. Review articles and meta-analyses can provide a more comprehensive understanding by synthesizing findings from multiple studies.

What role do review articles and meta-analyses play in the field of nutrition research?

Review articles and meta-analyses are important because they compile and analyze findings from multiple studies, helping to identify trends and reconcile apparent contradictions, thus providing a more holistic view of the evidence.

Outlines

00:00

🤔 The Confusion of Nutrition Research

This paragraph discusses the complexity and contradictions often found in nutrition research, highlighting the difficulty in determining whether certain foods or supplements are beneficial for health. It uses the example of red wine, which has been both praised and criticized in various studies. The paragraph emphasizes the importance of understanding the nuances of research methods, such as the differences between studying effects in animals versus humans, and the potential for other factors to influence results. It also points out the challenge of translating research findings into practical dietary advice due to the variability of study outcomes.

05:01

🍇 The Case of Raspberries and Blood Pressure

This section delves into the contrasting findings from two studies on the effects of raspberries on blood pressure. A 2011 Chinese study using raspberry extract in rats found a positive impact, while a 2013 Finnish study using berry puree in humans with risk factors for heart disease found no effect. The paragraph explores the reasons for these discrepancies, such as differences in study subjects, methods, and the potential interference of other ingredients in the berries. It also touches on the limitations of animal models and the complexities of human behavior and diet, which can affect study outcomes.

🍷 The Red Wine Resveratrol Paradox

This paragraph examines the conflicting results from studies on resveratrol, an antioxidant found in red wine. A 2012 randomized controlled trial suggested that resveratrol supplements improved cardiovascular health, while a 2014 observational study found no such effect. The paragraph explains the differences between these study types and the implications of their findings. It also discusses the importance of considering the dosage and bioavailability of nutrients, as well as the potential for supplements to be more effective than dietary sources.

🥕 The Beta Carotene Conundrum

This section presents the surprising findings from studies on beta carotene, a precursor to vitamin A found in foods like carrots. While observational studies indicated that a diet rich in beta carotene could lower lung cancer risk, clinical trials giving beta carotene supplements to smokers actually showed an increased rate of lung cancer. The paragraph explains how high doses of beta carotene can act as a pro-oxidant, promoting cellular damage, and highlights the importance of context and dosage in nutritional studies.

🧐 The Broad Question of 'Good for You'

The final paragraph addresses the broad and often misleading question of what it means for something to be 'good for you' in the context of nutrition research. It emphasizes that studies typically focus on specific health outcomes rather than a general assessment of goodness. The paragraph uses the example of alcohol, which can have both positive and negative effects depending on the amount consumed, to illustrate the complexity and nuance of nutritional science. It concludes by encouraging a cautious interpretation of individual studies and a holistic view of the evidence.

Keywords

💡Nutrition Research

Nutrition research refers to the scientific study of the relationship between food and health. It is the process of investigating how nutrients and other food substances affect the body. In the video, the theme revolves around the complexities of interpreting nutrition research, which often leads to conflicting advice on what is 'good' or 'bad' for health. The video script discusses how the results of nutrition studies can be difficult to translate into practical advice due to imperfect comparisons and varying study designs.

💡Red Wine

Red wine is a type of alcoholic beverage made from dark-skinned grape varieties. The script mentions red wine as an example of a food product that has been the subject of conflicting health claims. It highlights how studies have variously reported red wine as beneficial or neutral in terms of health effects, particularly concerning cardiovascular disease.

💡Resveratrol

Resveratrol is a natural antioxidant compound found in grapes and red wine. The video discusses how studies on resveratrol have shown mixed results regarding its effect on cardiovascular health. It exemplifies the challenge of interpreting the outcomes of different types of studies, such as randomized controlled trials and observational studies.

💡Randomized Controlled Trials (RCTs)

Randomized controlled trials are considered the gold standard in scientific research, particularly in medicine. They involve randomly assigning participants to either an experimental group or a control group to test the efficacy of an intervention. In the script, an RCT is mentioned as a study type that found resveratrol supplements improved cardiovascular health indicators, contrasting with other study types.

💡Observational Studies

Observational studies involve collecting and analyzing data without manipulating variables, as opposed to experimental studies. The video script refers to an observational study that did not find a cardiovascular benefit from resveratrol, highlighting the differences in results that can arise from different study methodologies.

💡Beta Carotene

Beta carotene is a precursor to vitamin A and is found in many fruits and vegetables, such as carrots and sweet potatoes. The video uses beta carotene to illustrate how observational studies can suggest health benefits, while clinical trials may reveal risks under certain conditions, such as the increased lung cancer rate in smokers who took beta carotene supplements.

💡Antioxidant

Antioxidants are substances that can prevent or slow damage to cells from reactive oxygen species. The script discusses resveratrol as an example of an antioxidant and how it is thought to help prevent potentially damaging chemical reactions in cells, but also notes that high doses of beta carotene can act as a pro-oxidant, leading to cellular damage.

💡Pro-Oxidant

A pro-oxidant is a substance that has the opposite effect of an antioxidant, promoting chemical reactions that can lead to cellular damage. The video script contrasts the roles of antioxidants and pro-oxidants using beta carotene as an example, where high doses can act as a pro-oxidant, especially in the context of lung cancer risk in smokers.

💡Cardiovascular Disease

Cardiovascular disease refers to a class of diseases that involve the heart or blood vessels. The script frequently mentions cardiovascular disease as an outcome measure in studies about the health effects of red wine and its compounds like resveratrol, emphasizing the complexity of understanding food's impact on health.

💡Health Outcomes

Health outcomes are the results or consequences of a disease or condition on an individual's health. The video script discusses how nutrition studies focus on specific health outcomes, such as rates of stomach cancer, blood glucose levels, or cholesterol levels, to measure the effects of diet or supplements on health.

💡Alcohol

Alcohol is a psychoactive substance found in beverages like beer and wine. The script uses alcohol to illustrate the nuanced effects of substances on health, noting that while light or moderate alcohol consumption may have positive effects on cardiovascular health, heavy drinking can have detrimental effects on various aspects of health.

Highlights

The complexity of determining whether food or supplements are beneficial due to conflicting information and research.

The example of red wine's health benefits being both supported and refuted by different studies.

The difficulty in translating nutrition research into practical advice due to imperfect comparisons and differences between compounds and whole foods.

The importance of examining studies closely to understand the context and reasons for differing results.

The contrasting findings on the effects of raspberries on blood pressure between a Chinese study using rats and a Finnish study with humans.

The potential interference of other ingredients in berries with the effects of raspberry extract alone.

Differences in study outcomes between animal models and human subjects.

The limitations of using animal models and the challenges of replicating those conditions in human studies.

The role of individual studies as pieces of a larger research puzzle in nutrition.

The contradiction in findings between a 2014 study and a 2012 study on the effects of resveratrol in red wine.

The difference between randomized controlled trials (RCTs) and observational studies in human nutrition research.

The potential for high doses of beta carotene to have a pro-cancerous effect, contrasting with its presence in healthy foods.

The importance of understanding the specific outcomes and markers related to health issues in nutrition studies.

The nuanced effects of alcohol, with potential benefits for cardiovascular health but risks for other health issues.

The necessity for scientists to consider the whole body of evidence in nutrition research due to the complexity and variability of findings.

The public's interest in nutrition research and the desire for control over health through diet.

The recommendation to approach individual nutrition studies with caution and skepticism.

Transcripts

[♪ INTRO ]

It seems like it’s practically impossible to get a straight answer on whether a given

food or supplement is good for you.

First they say red wine is good for you.

Then there’s a headline announcing that it doesn’t do anything, and wait, isn’t

alcohol supposed to cause cancer?

If you wanted to change up your diet to accommodate all the latest news reports, you wouldn’t

get very far before you’d run into all kinds of contradictions.

I mean, you can’t both drink and not drink alcohol at the same time.

And the problem goes deeper than the over-exaggerated headlines on cable news.

Often, the way nutrition research is done makes it really hard to translate the results

in to practical advice because of imperfect comparisons.

The effects of one compound might not be the same as the effects of the entire food.

What happens in animals might be different from what happens in humans.

And a food that’s good for you in some ways might be bad for you in others

But it is possible to untangle all that by examining these studies more closely.

You just need to know what you’re looking for.

Take what happened with raspberries not too long ago.

In a 2011 study, researchers in China found that red raspberries could improve blood pressure.

Annnnd then in 2013, a team in Finland found that fresh berries didn’t affect blood pressure

at all.

There were plenty of differences between these two studies, though — and plenty of reasons

they might have had different results.

The Chinese study used raspberry extract, and was done on rats … specifically, a strain

of rats prone to high blood pressure.

Whereas the Finnish study used berry puree, and the subjects were humans with symptoms

that increased their risk of heart disease, like high blood pressure.

The first problem with comparing them is that the other ingredients in the berries could’ve

interfered with the effects of the compounds in the raspberry extract alone.

Then there’s the whole “humans vs other animals” thing.

One reason scientists use animal models is that you can control everything about them.

You can administer every speck of food they eat, control how much they exercise, and monitor

them day and night.

Try to do that with a human and see how long it takes to get punched in the nose.

But that means in this case, the humans who got the berries might have been doing or eating

something else that negated the effects.

Or hypertension-prone rats might be more sensitive to the blood pressure-lowering effects of

berries than normal, if somewhat unhealthy, human beings.

Comparing those two studies is a little bit like comparing apples and oranges … or apples

and raspberries, I guess.

Different types of studies are important.

It’s usually much easier and safer to test things in other animals before moving on to

humans, and scientists in all fields of research rely on multiple lines of evidence to form

conclusions.

That’s how science works!

But when it comes to nutrition, most individual studies are intended as a piece of a larger

research puzzle, not something for the home consumer to take to the grocery store.

Studies on humans might be easier to translate to your life, but even those are fraught with

complications.

Like when a 2014 study on red wine contradicted the findings of another paper from two years

earlier.

Both studies were specifically concerned with a compound in wine called resveratrol, which

is an antioxidant — meaning it helps prevent potentially damaging chemical reactions in

cells.

In 2012, a randomized controlled trial by Hungarian researchers found that adults who

received resveratrol supplements showed an improvement in a bunch of signs of cardiovascular

disease.

Randomized controlled trials, or RCTs for short, are the closest you can get to a controlled

experiment in humans without the aforementioned nose punching and a whole passel of ethics

violations.

Participants are sorted into groups and statistically randomized so the experimental and control

groups are as uniform as possible.

Then you give the experimental group the food or supplement or specialized diet you’re

studying, which should ideally be the only thing that’s different between the two groups.

And this RCT seemed to show that resveratrol made a difference.

But then, in 2014, an observational study of adults in Italy didn’t find any effect

of resveratrol on signs of cardiovascular disease or mortality.

Observational studies are different from RCTs.

They aren’t really experiments — they involve gathering data that’s already out

there, in this case by interviewing people about their eating habits and analyzing their

urine.

RCTs are usually thought of as the most rigorous type of human study, but that doesn’t mean

they’re always right and observational studies are always wrong.

The 2014 observational study found that while participants had a lot of resveratrol in their

diets, like from wine, the stuff might not have reached a high enough concentration in

their bodies to have any biological effect.

So the lesson there might be that supplements are more effective.

Which brings us to a fairly infamous example from the field of cancer nutrition.

Beta carotene is a dietary precursor to vitamin A found in foods like carrots and sweet potatoes.

A body of evidence from multiple observational studies suggests that eating fruits and vegetables

rich in beta carotene lowers the risk of lung cancer.

Which was the justification for a number of clinical trials, including one in Finland

in 1994 and one in the US in 1996, which gave beta carotene supplements to smokers.

Except, the smokers who got beta carotene had a HIGHER rate of lung cancer.

You really don’t want to give your study population cancer, so this came as a bit of

a shock.

In the fallout, it was found that beta carotene in high doses could actually act as a pro-oxidant

-- a compound that’s the opposite of an antioxidant, and promotes chemical reactions

that lead to cellular damage.

So the observational studies showed that carrots are good for most of us, but the clinical

trials discovered that under specific circumstances, high doses of beta carotene have a pro-cancerous

effect.

These findings weren’t exactly contradicting each other … it was just another case of

comparing the wrong things.

So that’s another thing to look out for with nutrition studies.

When you dig into the details, findings that seem contradictory might turn out to be building

on each other.

The final -- and probably most important -- question to ask when you see a report announcing that

something is good for you is, what does “good for you” even mean?

There’s no universally agreed upon definition for it, and it’s never what researchers

specifically set out to study.

Trying to figure out whether something is “good for you” is just too broad.

Studies might look at rates of stomach cancer after a certain number of years, blood glucose

levels, cholesterol levels, or any of the other incredibly specific markers related

to cancer or diabetes or obesity or some other health issue.

Scientists who study nutrition call these outcomes, and they’re probably the most

important thing to look for in any nutrition study.

Going back to the wine example, red wine contains a whole bunch of plant compounds that are

targets for nutrition research — resveratrol is just one of them.

At the risk of stating the obvious, wine also contains alcohol.

And alcohol itself might actually be good for you in some very specific ways.

A 2002 analysis of several dozen studies of the effects of wine and beer found that overall,

wine drinkers were less likely to die from heart disease, or to experience other, less

fatal heart problems.

But the association was there for beer drinkers too.

It was statistically weaker, but clearly the effect wasn’t just coming from the special

plant compounds in wine.

This finding has cropped up more than once, and there’s enough evidence that some nutrition

experts might recommend light or moderate alcohol consumption to help prevent cardiovascular

disease.

Does that mean alcohol is good for you?

Well.

I mean.

It’s alcohol.

Even if it helps your cardiovascular system, it also messes with your liver, interferes

with fetal development, increases the risk for certain cancers, depresses your central

nervous system and a whole list of other things.

In some of these cases, the dose makes the poison.

The evidence points toward light or moderate drinking having certain positive effects,

but heavy drinking being bad in basically every way.

While alcohol is an extreme example, it’s not hard to find cases where a particular

food or nutrient has a positive effect on some outcomes and a negative effect on others.

These studies aren’t contradicting each other because they’re not trying to answer

whether something is universally “good for you.”

But when the findings show up in the news, sometimes that nuance gets lost in translation.

When it comes to nutrition research, there are so many seemingly contradictory findings

coming out all the time that even the scientists publishing them need to step back and look

at the evidence as a whole.

That’s why the field is full of review articles and meta-analyses.

The process of science is pretty much always this messy, but for some reason with nutrition

it’s on public display.

Maybe that’s because we want to be able to justify our craft brew hobby by believing

it’s healthy, or because we’re always looking for ways to live longer and stave

off diseases.

Maybe it’s because what we eat feels like the one thing we can control in a world full

of unknown risks.

But it helps to take every individual nutrition study with a grain of salt.

Not too big a grain, though — I just read that salt’s bad for you.

Or was it good for you?

Thanks for watching this episode of SciShow, which is produced by Complexly.

For other awesome Complexly videos about nutrition and health research, check out Dr. Aaron Carroll

over at Healthcare Triage.

[♪ OUTRO ]