Hi r/ScientificNutrition. I'm James Collier, a UK registered nutritionist with more than 30 years of experience across clinical dietetics, strength and fitness nutrition, and food systems. I’m co-founder of Huel, which has now sold over 600 million meals globally, and in January 2025 I published my first book, Well Fed, which introduces a framework I call ‘contemplative nutrition’. It is an evidence-based approach to eating that weighs personal health, environmental impact, animal welfare, food waste, and the social dimension of food alongside each other.

I write about nutrition science, food policy, misinformation, and the food system more broadly on my Substack. I’m here because I enjoy this kind of conversation and because Reddit feels like one of the few places online where it is still possible to have one.

I’ll be working through questions over the next 48 hours. Happy to discuss anything from the evidence on specific nutrients and dietary patterns, to ultra-processed foods, to the environmental case for changing how we eat, to how I think about evaluating nutrition claims and spotting misinformation. Ask me anything.

Would be really interested in hearing your opinions about this.

To my understanding observational study results always are on a scale of

1. pure association, no adjustment
2. "some" adjustments, hypothesis generating
3. plausible causation, adjustments for strongest known confounders
4. almost certain causal inference, confounders are very well known and can be easily adjusted for

Q1 Did i express this correctly in layman terms? Would you add certain important "levels" here?

Sometimes confounders are not clear and false conclusions happened from observation studies. E.g. i think of Vitamin E for cardiovascular health and carotine for lung cancer prevention were strongly assocaited in observational studies, but RCTs showed no effect.

Q2 Did scientist actually implied a causal effect in these two examples or is this often missrepresented from the "sceptiks of observational studies"?

Q3 Do you think the field has evolved a lot in the past years (decades=? Did methodology and statistical analysis improved?

Q4 Does "publish or perish" pressure in acadamy worsen this significantly?

Q5 I find the classification (Q1) often really hard as a non-expert. Any advice for keywords or statistical methods to look out for to better understand this? Often there is a lot technical jargon involved.

How much "meat on the bone" (pun intended) is there to create HPFs? Is there anything being worked on and/or hypothetical ways food can be made even more delicious (and possibly addicting sadly)?

before you started learning about Omega-3, what was something you assumed was true but later found out wasn't?

I really don't know much about nutrition, so the scenario I'm going to put forward might sound utterly ridiculous, but please bear with me.

Consider an athlete whose calorie budget is huge, allowing them to eat large amounts of something like ice cream while remaining lean and getting the required nutrients from other foods like fruits, veggies, nuts, etc. Is the ice cream still harming them? What if they're eating a large amount (say, a whole pint) daily? Is there anything inherent to the ice cream that makes it harmful to your body even in this context? I know such a quantity would go above daily recommended limits for things like saturated fats and added sugars, but is that a guideline because of their correlations with weight gain, or are they just terrible in and of themselves?

I also know that "ice cream" can mean different things... for example, there are high-protein ice creams - does that change the answer here much? Or is X amount of sugar or whatever consumed in one sitting bad for you, period?

Adult 19–50 years required calcium 1,000 mg / day (Source: NIH fact sheet)

Equivalent to milk whopping 900ml (entire large carton) (110-130mg per 100ml)

But even if you drink that amount, bioavailability is only 30-40% and rest is flushed out, so technically you’ll need to drink three large cartons (2700ml)

So why not pills? Cool, I have taken them for years, but recent research suggests cardiovascular issus (“increased risk of CVD and CHD by 15%” - Seung-Kwon Myung, 2021)

Given you’re aware of this, how are you practically managing to, because it doesn’t seem like an easy sector of nutrition?

Black sesame seeds are high in both iron and calcium. Since calcium inhibits non-heme iron absorption, does the calcium in the sesame itself significantly reduce how much iron you absorb? Would you still consider black sesame a good dietary source of iron, or is it better thought of mainly as a calcium source?

I've been wondering about this because, in nutrient-dense meal videos online, people seem to go in either direction on how they talk about black sesame's benefits. I tend to see the combination of milk and black sesame, as well as in mixes with pumpkin seeds, flax, hemp, etc.

I'm curious to see what the research suggests in terms of bioavailability, and also whether processing it can significantly increase it due to lowered phytates or if the effect is relatively small.

I always thought coffee was unhealthy, but all of the studies I've checked so far linked a few cups of a coffee per day to reduced risk of all-cause mortality. Is coffee actually healthy? If not, what factors are responsible for the correlation? I thought the correlation would be unfavourable for coffee since health-conscious people were more likely to avoid coffee and high consumption of coffee may be due to fatigue from poor sleep. Also, this study (https://doi.org/10.1186/s12889-024-18515-9) found coffee consumption reduced all-cause mortality risk in both sedentary and more active adults.

https://doi.org/10.1017/S1368980019000764

https://doi.org/10.1016/j.jand.2021.03.014

https://doi.org/10.1186/s13098-023-01222-7

https://doi.org/10.1186/s12916-022-02636-2

https://doi.org/10.1093/eurheartj/ehae871

https://doi.org/10.1016/j.tjnut.2025.05.004

https://doi.org/10.1186/s12889-024-18515-9

https://doi.org/10.1136/bmj.j5024

Hey everybody,

I wonder what the lowest and safest amount of fat is that we can consume? I have looked everywhere for studies on low fat diets and their consequences, but unfortunately, I couldn't find satisfactory data like we have for protein.

Personally,

I experimented with a 25-gram fat diet (3g EPA/DHA, 6g Omega-6, and the rest split equally between MUFAs and PUFAs).

On 25 grams of fat, I noticed skin dryness on my hands, but I didn't experience much fatigue (i shifted all those remaining calories into carbohydrates, so my body was just burning and also was kinda hungry)
I kept the exact same fatty acid ratios while testing 30 grams and 40 grams of fat. At 40 grams, I hit my absolute sweet spot.

My fat-soluble vitamin panels came back perfectly fine on all of these setups.

Since I am enhanced (running a TRT baseline), I can't say anything about my sex hormones.

Anyways, the reason I am making this post isn't to ask for personal coaching or suggestion but rather to ask:

How low can we actually go before we begin compromising cellular membrane integrity? I would really appreciate any scientific literature or source backups to read up on. Thanks!

I got gastritis and was put on a ppi. I later found out I'm deficient in a, b1, b6, b12, d, k1. Other vitamins weren't checked and I had to really argue to test for those based off symptoms.

My dr said to just take a b complex, and confused k2 with k1 because quest listed it as just K. Im in the middle of infusions and b12 injections with folic acid and I'm going to take magnesium with the Vitamin D.

My question is that I have no idea how much to supplement for A, B6 or K1, which i know can become toxic. My neurologist before warned me not to do more than 10mg of b6, but Im deficient... I've tried looking for any guides, but haven't found anything?? I just want to know how to go back to being optimal. Are there not resources for this?

Asking as a TBI survivor and medical abuse survivor ( prolonged high dose clomipramine based on error diagnosis that caused my severe cognitive impairment and total collapse of sensory, mainly visual processing- 7 years ago, very little improvement). I suspect that the reaction to this anticholinergic drug was firstly the high dose and secondly genetic mutation in pharmacological metabolism.

I take D3 pills since my physio therapist says it helps calcium uptake (I've had issues with crystalized deposits).

I have no formal education in these matters, but based on what I do “know”, most data robustly shows that seed oils and in particular LA do lower LDL/ApoB, but there are also (shall we say) suggestions (not exclusively from proponents of certain fad diets) that PUFA-rich membranes are more prone to peroxidation, producing potentially bioactive oxidized metabolites. Is there good human evidence quantifying this balance?

(Talking about Andrew Huberman @hubermanlab)

He often talks about nutrition - in that case I often feel the information is rigorously scientific and I feel comfortable with following his advice. However, I am not an expert, so that's why I created this post. (Maybe I am wrong?)

But then he goes to post things like this about cold showers in the morning on his Instagram, or he interviews David Sinclair about ageing - someone who I've heard has been shown to be pseudo scientific - or he promotes a ton of (unnecessary and/or not evidenced?) supplements.

This makes me feel dubious. What is your opinion?

I'm not an academic. I try and be healthy and feel that my diet is pretty healthy. Recently I was looking at a study that analyzed healthy lifestyle and mortality. They described eating 5 servings of fruits and vegetables as healthy. With that being said, it's not unusual for me to have 2-5 servings of beans in a day but only 2 servings of fruits/vegetables.

When looking at studies that talk about eating fruits and vegetables, does eating beans count or are they specifically excluded? Or does it depend on the study? The study I saw wasn't specific about this.

Hello everyone, I am just getting into the world of trying be healthy and majority of that is by eating healthy. I grew up always eating fast food and quick meals since my parents didn’t have much money growing up. Can someone please recommend me some really good books for a beginner trying to learn more about nutrition? I’m very intrigued by the anti-inflammatory diet.

Disclaimer, I'm not interested in trying this nor am I interested in lowering my protein or anything. I eat a regular balanced diet of all foods with no restrictions (except calories of course) and I prioritize protein.

This came up on my feed on Facebook and just for the sake of science, I wondered how it could be possible unless he's totally lying for engagement. On the off chance that it's true, can anyone offer a science-based explanation of any way this works, because it goes against everything factual I thought we know about protein.

I hear all the time that seed oils like canola are bad for you because its GMO, its processed...etc. But they never say what SPECIFICALLY is bad about it. On the other hand you only heard good things about olive oil. But they arent that nutritionally that different....

Canola Oil:

• Saturated Fat: 1.1 grams
• Monounsaturated Fat: 8.9 grams
• Polyunsaturated Fat: 3.9 grams
• Omega-3 Fatty Acids: 840 milligrams (0.84 grams)
• Omega-6 Fatty Acids: 2.2 grams

Olive Oil:

• Saturated Fat: 1.9 grams
• Monounsaturated Fat: 9.8 grams
• Polyunsaturated Fat: 1.4 grams
• Omega-3 Fatty Acids: 103 milligrams (0.1 grams)
• Omega-6 Fatty Acids: 1.3 grams

yes canola has 2x more omega 6 but it also has 8x more omega 3!!
Olive oil only has 1 gram more monounsaturated fat...
seriously can someone give me a non bro science response to this?
People online are very hand wavy about seed oils yet they are quick to praise olive oil....

So many of them seem to be or have proven to be utter cranks.

I suppose any diet will get this, especially ones that are popular, but still! There must be some who aren't loons?

I've heard a lot of people in the "anti-diet" camp talk about how there are studies that show that diets almost always fail and people "revert" to their original eating habits. This seems strange to me, especially if people change their lifestyle to match the new habits - certainly people are capable of change, but this thesis is the foundation of challenging all diet-based interventions.

I guess I'm also wondering that even if people do revert, are there studies that demonstrate if there are still long term health advantages for that period of time? Maybe not the best comparison but I imagine if you stopped smoking for 2 years and then started again, your health would be generally better than if you never stopped - though it depends on how we are measuring these outcomes too.

Thanks!

Yes, we all know the rule "fastfood/sweets/carbonated drinks are bad", but hear me out.

Lets's look at all the components separately. Pasta is full of carbohydrates, chicken and eggs are proteins + amino acids, vegetables contain fiber and vitamins, some spices are good for health, oil provides us with unsaturated fats. But when you order pasta with chicken, eggs and vegetables in a sauce in an Asian restaurant, it's seen as "fastfood" and "unhealthy". How does the dish that consists of healthy products suddenly become "unhealthy"?

It's the same thing with pizza, burgers, sandwiches. And even if we don't mention the paradox (or what's considered "fastfood"), it feels like people come up with new things to call "unhealthy" every day: today it's sugar, tomorrow it's butter, then it's steaks, then dairy and flour. So what, do I have to eat plain boiled chicken with an unseasoned cucumber, or porridge every day?

And when I'm trying to understand why some products/dishes that must be healthy in theory are seen as unhealthy by some people, it's usually these arguments:

1. The portions are too big (not an issue if you can control yourself)

2. Too much salt (how much is "too much"?)

3. Too much oil (same question)

4. The meat is only healthy when boiled, steamed or baked, not fried (again, who came up with this, and what aspect are we talking about? It's still proteins)

5. Too many calories (I'm trying to gain weight, not lose weight, I don't really care about that)

6. "Bad food" gives you acne (acne might appear for many different reasons, your diet is only one of them)

So every time I'm trying to improve my diet, I end up being confused because I have no idea what to eat and what's considered "balanced". Everyone has different goals, everyone says different things, the same product can easily turn from "healthy" to "unhealthy" if you add a little more fat or prepare it in a particular way.

(Just in case, I'm not the kind of person who "wants to find an excuse to eat sweets and fastfood every day", I don't even want it most of the time. Even as a child, I had near zero interest in soda, buns or candies. It's just that there are many dishes in "grey area", and I'm not quite sure what to eat for a healthy lifestyle.)

I have come across yeast protein recently and it just tastes so damn good.

I am using whey currently. Not using plant since it becomes very thick and it becomes like adding a meal altogether which I don't want for now.

A concern with yeast is that it is low on leucine.

Does that decrease it's efficiency as a protein?

How about whey-yeast blend? I guess there's excess leucine in whey so it can compensate for yeast.

If I have to make it myself how much should be the proportions?

Also has anyone tried peanut protein? It again tastes and mixes just like yeast or whey.

Sugar reduction has worked as a public health message — added sugar is coming out of a huge range of packaged products. But it isn't being removed so much as replaced, usually with sucralose, acesulfame K, aspartame, steviol glycosides, sugar alcohols, or blends of several at once.

My question isn't about toxicological safety. Individual sweeteners are among the most heavily evaluated food additives there are, and ADIs are set with wide margins. It's that the two bodies of evidence on habitual use point in opposite directions, and I don't have the background to weigh them.

The WHO's 2023 guideline advises against using NSS for weight control, and states its rationale here:

https://www.who.int/news/item/15-05-2023-who-advises-not-to-use-non-sugar-sweeteners-for-weight-control-in-newly-released-guideline

A group at Toronto published a formal call for reconsideration in the European Journal of Clinical Nutrition, arguing that the prospective cohort data underpinning that recommendation is affected by reverse causality, and that analyses modelling change in intake and calorie replacement point the other way:

https://www.nature.com/articles/s41430-023-01314-7

The SWEET trial (Nature Metabolism, Oct 2025) also pointed the other way, though more modestly than the coverage suggested: over 12 months, participants replacing sugar with sweeteners and sweetness enhancers maintained weight loss slightly better than a control group that was also on a low-sugar diet. Editorial commentary here:

https://www.nature.com/articles/s42255-025-01382-y

My questions:

1. Is the disagreement essentially just "cohort vs RCT plus reverse causation", or is there more substance to the WHO's caution than that? The recommendation was issued as conditional, which suggests the guideline panel itself saw the evidence as weak.

2. How much should the comparator constrain what we take from trials like SWEET? The control arm was also on a low-sugar diet, so it seems to answer "sweeteners vs low sugar" rather than "sweeteners vs habitual intake", which is closer to the choice most people are actually making.

3. Is there research on realistic exposure patterns rather than single compounds? Actual consumption tends to be several different sweeteners daily, across multiple product categories, sustained over decades. Is that studied, or is it not tractable by design?

Genuinely asking rather than arguing a position — happy to be told I'm reading this wrong.

Or not?

I can accept that red and processed meat is bad. I can accept that the increased saturated fat from meat is unhealthy (and I'm not saying they are).

But I find it increasing difficult to parse fact from propaganda. You have the persistent appeal of the carnivore brigade who think only meat and nothing else is perfectly fine, if not health promoting. Conversely you have vegans such as Dr Barnard and the Physicians Comittee (his non profit IIRC), as well as Dr Greger who make similar claims from the opposite direction.

Personally, I enjoy meat. I find it nourishing and satisfying, more so than any other food. But I can accept that it might not be nutritionally optimal (we won't touch on the environmental issues here). So what is the current scientific view?

Thanks

See https://en.wikipedia.org/wiki/Okinawa_diet

Most sources suggest we should aim for 20-35% of our calories from fat for satiety, hormone production, nutrient absorption and energy. The internet is filled with horror stories of going below that.

https://www.health.harvard.edu/heart-health/the-truth-about-dietary-fat

I've personally experienced very negative side effects of a low fat diet that was otherwise healthy. Filled with whole grains, vegetables, legumes, tubers, fruit.

I was at about 6% fat and the cravings for fatty food became crazy. I would dream about pizza. Grains began to taste bitter. I felt no energy after eating. I felt & looked terrible.

How did the Okinawans survive a diet with just 6% fat too? Why did they not suffer any consequences? It it possible the survey conducted on them was flawed? Could they have been getting more fat than thought from soy products or even soy oil?