What are the *risks* of losing weight (when overweight)?

This posts relates solely to people who are overweight or obese and who have excess weight to lose. Those who are at a healthy weight have different risks from losing unnecessary weight.

Edit: 30 May 2025 - nice article by Bethany Brookshire in Scientific American, New powerful GLP-1 drugs drop a lot of weight fast. How does that affect health? (About the effects of weight loss, particularly dramatic loss, on muscle and bone).

Edit: 29 June 2025 - I suppose enough people have recently been losing weight with the various Mounjaro / Ozempic type drugs for this question to be updated.

I've not heard of any additional atherosclerotic risks from people losing their excess weight. This could be because

• There is no additional atherosclerotic risk from losing weight
• The risks have not yet been reported or have not been specifically linked to the weight loss
• It's still too soon for any additional atherosclerotic risks to become apparent.
  

There may be other risks / side effects (adverse effects) from using these medications but this post is solely about the resulting loss in bodily mass arising from any method used to lose weight (fat).

Original post

I've sent an email to the World Obesity Federation to ask. My sciencey background never brought up this facet of weight gain / weight loss but I have occasionally wondered. 

If transporting fats around the body when putting on weight can lead to atherosclerotic damage and high blood pressure can't the same thing happen when losing weight as, from a 'transport infrastructure' point of view, there's no difference - fat, in the form of lipoproteins, is whizzing around in the blood whether it's about to add to or be taken from adipose tissue.

Here's what I sent, if I get a reply I'll add the gist of it.

I am trepidatiously adding 'weight loss' to the labels for this post, knowing that this will very effectively bring a lot of spam commenters to my yard ;)

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Hello :)

I'm curious to know about the risks of losing weight (the benefits seem fairly obvious). As a fat person I have plenty of fat stores, which initially grew because fats (directly or derived) from my diet would have been transported around in my blood and eventually stored in various adiposits. Presumably some will also have been laid down atherosclerotically en route. Bummer. I expect we'll find out in a few years. Probably not that many as I'm 51.

If I begin to lose weight wouldn't the exact same process happen in reverse? A bit of metabolism will free up some of my lard which will then lipoprotein its way around my bloodstream before eventually being breathed out as CO2. Presumably in doing its circulatory rounds some of it could also contribute further to any atherosclerosis.

So is losing weight quite a dangerous undertaking? Prevention certainly better than cure I suppose.

Also, would I then flood my system with all the fat-soluble vitamins? Not too bothered about D or K, but I might want to avoid self-overdosing on Vits A And E. Presumably there will be other fat-soluble things that pop out into my bloodstream, much like a molecular version of ancient mammoths being released from the melting permafrost.

My retweet of a tweet in a thread by Foone about composting the
rich, rather than eating them (Compost the rich, don't eat the rich)

Presumably in returning to my bloodstream these fats will make it thicker and stickier, adding a blood pressure risk to weightloss proceedings. Possibly one should lose weight very slowly. Or maybe take blood thinners while doing so.

I'd also presume that the relative risk weighs (ha!) more in favour of losing any excess weight but I don't think I've ever seen this aspect of risk considered. 

Can you point me to any research in this area (I have a degree in biochemistry* and have worked in a lipid chemistry lab so am comfortable with academic literature).
 
Thanks
Jo

*Pedantically my degree is B.Sc (Hons) Combined Studies because that's what the modular degree was called (you could also do Combined Arts). My degree is in Biology, Psychology and Computer Science. I then did a Masters degree in Neuroscience. Given that neuroscience kinda covers biology, psychology and computer science you might imagine some great intentional plan but no - entirely by accident. I don't think I'd even heard of the word neuroscience until graduating and someone suggested it as a (suddenly rather obvious) follow-up.

Quick random thoughts on Vitamin D

I'm writing this at a conference so treat it as provisional as I'm on battery power and not doing my normal fact-checking. Bits in pink are bits I need to reference.

It's a while since I've really looked in any depth at the evidence for, or against, Vitamin D as something that people might want to use as a supplement. My interest in it stems from my time at Diabetes UK when there were a few questions from people about its particular value as something that might generally 'help' either in preventing diabetes from starting, or reduce complications or other helpful things.

At the time I first started looking into this I don't think there had been any intervention trials where people (with a particular type of diabetes) were split into groups, one lot given Vit D and the other not and the outcomes compared.

There were plenty of studies looking at Vitamin D status (eg how much Vitamin D or its metabolites is zinging around in your blood) and outcomes, which were interesting, but I never really felt I understood what Vit D status tells you. Vit D exists in several forms - there are one or two coming in via diet but they are immediately tweaked first by the liver to another form and then the kidney to another one (or possibly the other way around!). Your skin is also capable of rustling up a bit of Vitamin D all by itself.

So what's in your blood could be a consequence of what's in your diet or from the sun, or from what's going on with the enzymes that do this conversion. I also can't help wondering if, given that Vitamin D is a fat-soluble vitamin, gaining or losing weight makes a big difference to Vitamin D concentrations in the blood.

How good a predictor for health outcomes or diabetes complications etc is how much Vitamin D (metabolites) you have in your blood? Dunno.

But then I thought... fat soluble vitamins

I seem to remember that Vitamin A, essential for retinal goings on etc, can be a bit of a problem if you have too much of it. Vague recollections of giving polar bear livers a swerve as the content of Vitamin A can floor you. Vitamin A is fat soluble.

Vitamin E was touted as some life saving thing for people who'd had heart attacks I think? There was a trial looking at Vit E with some other vitamins or medication and it turned out that it wasn't such a great idea to use this. I mean obviously you need some of it but 'some of it being good for you' doesn't translate, not that surprisingly, to 'lots more of it is therefore also good for you'. Vitamin E is fat soluble.

Vitamin K plays an important role in blood clotting and I was surprised to learn recently that eating too much spinach (rich in Vitamin K) was perhaps contributing to unexpected INR (international normalised ratio - which is how the speed of blood clotting is measured) in someone using warfarin. High Vitamin K foods interact with warfarin, which can be potentially a bit of a problem. Vitamin K is fat soluble.

Are fat soluble vitamins something we want to be a bit more careful with, in terms of hoovering them up as supplements? I suppose to answer that I need to avoid positive confirmation bias of happening to know off the top of my head which are the fat-soluble vitamins and find out what dangers there are from all the water-soluble vitamins. To be honest I thought most of them just got peed out but I expect I should mug up on it.

Anyway, unintended consequences and all that - apparently Vitamin D supplementation can negatively affect your lipid profile. I suppose I should go and look up the reference for that, I hate it when people don't cite stuff properly...