Plateau on mounjaro

[NicPapr25]

SW 117kg
CW 91kg
Has anyone had experience of reaching a plateau on MJ? I have remained the same weight now for 1 month, I am doing the same amount of exercise and same food intake. Currently on 5mgs, not experiencing any real food noise so reluctant to up dose, previously I had been losing 1kg per week, so bit disheartened that nothing in last few weeks.

I read that use of ketone should be temporary and long term causes acidosis which is dangerous for body. Fat is a better source of energy for brain.

Nope the brain needs either carbs or ketones can’t use fat!! Agree not ideal longer term, best to have over 70-80g carbs a day.

Someone told me I need fat for energy if not having carbs as protein is not best energy source. He goes to gym and lifts weights. I didn't look it up to be honest, just went with it and actually have more energy and satiety if I add mct oil to my shake.

Yes there are recent studies proving fat can be used by neurons https://www.nature.com/articles/s42255-025-01321-x

The body has a store of carbs in muscle glycogen and the liver, it’s quickly accessed but it’s used up quite quickly - think of marathon runners hitting a wall. There is also a massive store of fat in adipose tissue but it’s less easy to access - fine for lower intensity activities but less good for running.

re: protein, yes the body can convert it to energy if needed but it’s a less good energy source, more helpful for muscle and cell repair. This is why it’s important to eat a balanced diet and not 100% protein! Around 100g of carbs a day is enough unless doing masses of high intensity training. I’ve tried being in ketosis (very low carb) and I just don’t have the energy to run. I also think it would be harder to built muscle. Tbh I don’t think no carbs is healthy as then there would be no fruit or veg.

re MCT oil - I thought that was more around making it quicker to get into ketosis?

the brain needs either carbs (from food) or ketones (body makes ketones when carbs are low). The brain also uses fat (which is what what study is saying). Note that study is in mice.

I’ve hit a couple of plateaus over the 5 months I’ve been on WLIs, both times have coincided with terrible constipation and needing to adjust what I eat. I think I’m hitting another one BUT I’ve lost 20kg since mid July and I’m the lightest I’ve been since I got married 12 years ago! I agree with PP that I try to see plateaus as maintenance ‘test’ windows rather than anything to panic about and it gives me a little reminder not to let old habits creep back in!

If you're not having carbs and so carbs aren't available for energy, (so you've used up all the glucose stored as glycogen in your muscles) then your body breaks down stored fat (not fat in the bloodstream) into ketones, which are your body's primary alternative form of energy. Your body and brain are quite happy to use ketones as an energy source. This is ketosis, which I'm sure you're familiar with.
Your body can break down protein in muscles to use as fuel (it can make glucose from protein), but it isn't very good at it. This is why you lose muscle mass when you diet.
So you're friend at the gym is correct when he says you use fat for energy if you have no carbs, and that protein is not great for energy. But this is in relation to fat and protein deposits in the body being used, not dietary fat and protein.
That 2025 research paper you linked to is a bit of a red herring. That is talking about a new discovery that lipids circulating in your bloodstream have been discovered to have a direct function in brain cell activity. That's a bit different to suggesting fat is a direct energy source. 👍

I personally consider my diet to be low carb. I don't eat bread, rice, potato or pasta (or obvious simple sugar like cakes and sweets). I do however eat loads of vegetables and salads.
Otherwise I don't generally restrict what I eat and don't count calories. Eating this way has proven successful for me with weight loss.

That’s low carb, not no carb and it’s likely to be over the 80g a day or so you need.

Yes because it's ethically not possibly to test the human brain eg they chopped it up to stain for genes in this study. They have quoted a relevant human research trial based on the specific gene deficiency. Yes the brain does use fat, but previously you said it can't. There are lots more articles out there but I don't have time to quote them.
MCT is an energy source (fat), it helps maintain ketosis for those who go very low carb. Lots use it in a bulletproof coffee, it helps with satiety.

Yes but to get stored fat you need to eat fat and also its broken down and converted into fat from excess sugar/carbs. I actually do have carbs but on a morning I would have a shake with only protein and found I was tired on it and at many times dizzy and shaky. It was my work colleague who lifts weight suggested adding fats to use as an energy source if im reducing carbs. Fats definitely give energy as when I've added fat, my energy increases. I've read and seen podcasts that women and men are different with ability to utilise stored glucose and its not as effective for women.

To get stored get you need to eat in a surplus, even if you only eat carbs (or protein) will still be stored as fat.

Carbs are easier to access as an energy source before exercise, and little danger of being stored as fat if there is an overall deficit.

re: consuming fat as fast energy source - yes the body will use this before stored fat but can’t see any advantage of this (in terms of weight loss) over a small amount of healthy carbs (if dizzy / shaky in a workout).