Correlation Fat gain, Fat % gain, Lean mass gain

[Olav]

Say I am 100kg 28% fat.  If I gain 1kg fat.  Will I weigh 101 kg and have 29% fat? 

Or will there be some additional gain in other tissues?  How much?

In the long run, will muscle mass increase additionally to "carry" the extra fat?  How much?

Does fat and lean mass tend to vary together (Thinking that perhaps it is difficult to gain lean mass with a calori deficit).

The background for the question is that both fat and lean mass are increasing, and I am not sure if I am actually more musculus.

[Heybales]

Considering Lean Body Mass (LBM) is everything BUT Fat Mass (FM) - you can gain LBM and not one bit of muscle mass.

If you start doing cardio, and body responds to it by storing more glycogen in muscle, which always has attached water - you just increased LBM and weight, and no muscle mass.

Same with blood volume increase when it gets hotter and body needs to cool more - total water gain in plasma, increased LBM, no muscle mass.

Your exact figure example is exactly that. If you gain 1 kg of fat, then that is the result.

But sounds like you are more curious, when you gain fat, do you also gain muscle. Don't have to, most people have enough muscle to take on additional load of probably more than several pounds of fat. They'll just slow down to handle it with what they currently have.

If you are a runner or other cardio sport, pushing the edge with your pace and current weight and total muscle usage, and you increase the fat load, then yes you would have to increase the muscle mass to keep the pace the same.

No one can answer your question, way too many variables, and genetics.

By no means do they vary together by same amount. For instance, very little water in fat cells, hence the reason much better long term energy storage compared to carbs.

So you can lose FM, and LBM barely drops. Lose enough though, and now you don't need as much blood volume, missing water, don't need as much carbs for energy unless you kept your exercise efforts just as intense, ect.

Also, depending on how you coming to conclusion you are increasing both, be aware bodyfat scales, the good ones, if used correctly, can be upwards of 5% accurate. Most are not, and neither are they used correctly with exact same hydration level (and water in body is ...?).

DEXA scan is only way you'd be able to tell outside a very long set of estimated BF% data points, to average out the noise of inaccuracy.