Weight Fluctuations

Wondering if anyone have experienced and can explain this: The combination of:

+a hard long run (2-3 hours, combo of lower and higher Z3). Same for a 4-5 hour outdoor ride at Z2 with z4/5/6+ sprinkled in.
+2-3 weeks into a training cycle (3 weeks of build/1 recovery), typically 450-500 TSS weeks
+followed by alcohol and carb/fat combos

=typically sees my weight go up by 4lbs for a couple of days, then goes back to normal (i.e. the 4 lbs disappear).

Can anyone explain what/why that is? I figure it has to be the body holding on to water, but is there inflammation or an excess lf glycogen storage at play too as a reaction to the stress to the body? (Alcohol isn’t exactly good for recovery either). More curious than anything at what’s behind this rapid weight gain/weight loss phenomenon.

Its natural for weight to fluctuate throughout the day by around 2kg (4lbs). Normally you’ll weigh least just out of bed and gain it over the course of the day as you naturally rehydrate. There can be exceptions due to dehydration, during a long/ hard ride etc.

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I see the same behaviour. After a hard ride I know my weight will rise with at least 2kg for a few days. I think it is due to inflamation which makes the body retain water.


How does the carb intake compare following your hard run/cycle to your normal training routine? Is it that maybe you’re glycogen depleted up to and including the hard effort, and then carb load afterward to replenish - that will boost your body weight just by the water required to hold the glycogen.

Yes - I see the same thing after particularly hard efforts. Often up 2-4 lbs for a couple of days despite being well fueled coming in and in calorie deficit for the day. I read somewhere it could be inflamation/water…

Blood plasma volume and RBC volume increase perhaps.

Some stock text I often send to clients. Might be handy for you!

What happens to a person when they momentarily add the following things to their diet above and beyond whatever they’ve been regularly doing?

  • Carbs : 1-3 pounds with first noticeable difference within a few hours to a day or two, depending on if it causes GI slowdown. More towards the 1-2 days side of things if no immediate gut content retention.
  • Water : Immediate weight gain, followed sometimes by weight loss due to electrolyte washout, with no net change long term. No larger effect than the weight of the water itself. Usually smaller.
  • Protein : If constipating, hours to a couple days. Could be marginal to many pounds if very constipating. If not, then probably no change noticeable at all.
  • Salt : Usually within hours to 24 hours, large immediate jump in weight, often followed by quick return to “normal” within 24-48 hours. Can be 1-4 pounds depending on magnitude of excess sodium consumption.
  • Fats : 4-10 days, and usually requiring pretty large excess to allow anything to be noticed, barring any constipating effect of high saturated fat consumption. Healthy fats will have no constipation effect and likely are invisible on the scale for at least 2 or 3 days.
  • Creatine : Within hours a small increase, that continues slightly and then remains elevated by 1-4 pounds depending on dose and person. Similar to sodium, but without the immediate washout effect because people continue taking it.
  • Alcohol : decreased weight within 2-6 hours (1-5 pounds), remains depressed 12-48 hours or longer if hydration isn’t replenished.
  • Caffeine : Similar to alcohol, but much less pronounced.

Remember, there is a dose-response relationship. Just like taking one sip of light beer is unlikely to make even the lowest-alcohol-tolerance person feel anything, consuming 100mg extra sodium, or 10g extra carbs isn’t going to cause anything measurable to happen on the scale.

Getting down in weeds
I wouldn’t get too down in the weeds about trying to tease out why the scale went up or down on any given weigh-in. You can drive yourself crazy and get really frustrated in the diet process that way. Best approach is to be consistent and just pay attention to trends that are much longer than 1 week. Ideally several weeks. Factors that might affect weight on the scale include, dietary salt, carbs, alcohol, water consumption, any GI slowdown related to various fiber, protein or fat types and magnitudes of consumption, hormones, stress, inflammation from training, average temperature at night, sweat rate in training, activity level the previous day, scale error, and the list goes on. SO, please definitely just assess trends, and not single weigh-ins unless you’re SURE there is something you can pinpoint that is beyond a shadow of a doubt affecting your weight meaningfully for the day. Examples might include:

  1. “I normally consume no more than 2000mg sodium per day but had a giant bowl of miso soup yesterday and probably topped 5000mg sodium, was thirsty all evening and now I’m swollen like a balloon.”
  2. “I just got really bloated and blocked up due to ovulation or pre-period hormones and I feel like I look 5 months pregnant.”
  3. “I’m dealing with some pretty severe constipation at the moment and haven’t been able to have a bowel movement in the last 48 hrs.”
  4. “I drank nothing but 6 shots of vodka last night and am clinically dehydrated.”

Re: Carb timing
You might be getting more carb replete with better carb timing around your training. Carbs are stored with water when they’re stored in the muscle and liver as glycogen so it’s quite common for folks to gain weight when their carb timing improves around their training. This is a good thing! Common times it happens: starting a higher carb diet & the week after returning from vacation where carb timing was suboptimal or nonexistent. Not to mention carbs tend to attract water in the gastrointestinal tract, so if ever you increase carb content of a diet, that can also cause a bump up in weight.

Re: Inflammation
I would bet if we did a cadaver study (impossible without killing you lol) it would NOT be inflammation that causes the increase in weight that you’re likely to see after a training day, compared to a rest day. I’d bet it would be an increase of carbs and water storage in your gut (literal food waste holding water inside the lumen of your intestines) and increased water within your muscle cells and liver due to slightly increased glycogen storage. Water is stored with glycogen, FYI. I would bet that 20% might be inflammatory swelling, tops. Might actually be more like 5% of the variation in weight unless you’re extremely sore in every muscle group in your whole body.

Happy to answer questions.


What an informative reply! Thanks for the thorough walkthrough.

I never really thought about the temperature at night being an issue. Could this be a reason why folks tend to gain weight in the winter time. I myself seem to lose weight much more easily in spring than in winter, even when I don’t see a noticeable increase in consumption.

That temp @ night comment was more in relation to sweat loss rates over sleep periods affecting next-day scale weight due. Just another variable in the heap of variables that affect morning scale weight, and a good reason never to get down in the weeds about a single weigh-in.

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So, I have wild weight swings day to day - like 2-5lbs - I track weight on the long term so it doesnt bother me too much. I hit my carb goals in a day but are you saying that more precise carb timing, with the same amount of carbs, could flatten those fluctuations?

No, not at all. Maybe the opposite, actually. If you have huge carb intake on huge training days, you might expect largest weight spikes after those days, assuming hydration is retained. Most of all, weight spikes in the range of 1-4% body weight are pretty common within 24-hrs and aren’t anything to be concerned with.


Ah ok that makes sense, thanks for the clarification!