Understanding Weight Swings

Most dieters are stumped when they notice their weight going up and down by a couple of pounds. Here’s my last few weeks. I weigh every morning after I pee and before I take my shower. This post will attempt to explain some of the reasons for weight fluctuations.

Reasons for Weight Fluctuations

There are a lot of explanations for our daily weight swings. Some of these are probably understood by dieters, but others are more technical:

  • Salt variance
  • Caloric variance
  • Level of Hydration
  • Previous Day Exercise
  • Fecal matter
  • Glycogen Storage

Salt Variance

Salt comes in via differing concentrations in different foods. In keto, the salt from foods tends to be much less than the salt from processed/refined carbohydrate foods but there are notable exceptions like some cold cuts and cured meats. This is described here (Electrolytes, Water Retention, Low Carb Diets).

The variance in salt day-to-day will cause you to hold onto water weight until your body equalizes.

Feeling Salty? My n=1 Salt Experiment

If you are skeptical about the effect of salt on your weight, eat a jar of pickles or some ham.

A small jar of pickles has only 44 calories but 3000 mg of Sodium. A small jar of olives has 250 calories but 2600 mg of Sodium. I deliberately ate a jar of olives one day and a jar of pickles the next day and got my weight to go from 168.1 lbs to 171.1 in just two days. And that weight “gain” can’t be blamed on calories since my caloric intake on those days was below my typical energy expenditure (one of the days was 1400 calories and the other was 2200 calories). It was all about added salt.

I had about 3 cups worth of ham on Easter and went from 167.7 lbs Sunday AM to 171.0 on Monday AM. The ham had almost 5000 mg of Sodium.

Can We Eliminate Weight Variance from Salt?

It may be possible to eliminate this variance by being consistent in salt intake. I haven’t tried this so I can’t say. Does salt delivered in pickles work on a different way as the pickle gets digested than salt sprinkled on food?

It does appear that in my case it takes a couple of days for the weight gain from salt to be expelled.

There may be other connections. For an interesting account of the effect of salt on cosmonauts, see (The Connection Between Salt and Weight).

Caloric Variance

My day-to-day caloric variance is pretty wide. Here’s my last two weeks:

It may be surprising to many people, but numerically this has probably the least amount of effect. It would take over-eating by a significant amount over a long time to gain weight and it’s particularly hard to do on a day-to-day basis. Looking at the maths involved, if you ate an extra 100 calories that would at most turn into 100/3500 lbs of fat. That’s only 0.04 lbs.

Energy Expenditure Gets Up-Regulated

Your body tends to up-regulate your energy expenditure when you eat too many calories. Of course, over a long term you can over-stuff yourself constantly and get heavy – a strategy used by Strong Man competitors (Brian Shaw’s 12,000-calorie Strongman Training Nutrition Plan).

Your body can drop your metabolism when you eat too little. This is minimized with the Low Carb diet as long as you are not eating below your body’s ability to provide energy from fat (Hypophagia – How much fat can I lose in a day?). The missing calories get provided from body fat which tends to prevent metabolism from dropping.

It takes a consistent and long run at caloric decrease to drop weight. I’ve done it with Protein Sparing Modified fasting. The Low Carb diet itself tends to drop weight often due to less of a desire to overeat.

Level of Hydration

Anyone who takes their weight overnight will notice that their weight may go down several pounds from bedtime to after they pee in the morning. What you actually lose overnight is probably much less than a lb. Weight loss overnight is expelled as CO2 in your breath (Fat ‘breathed out’ of body via lungs, say scientists).

You may have noticed that if you drink a lot of water in the evening you might have to take a couple of trips to the bathroom overnight. If you get up later you may eliminate more of the water. I can be down weight on the scale on a Sunday when I sleep in late. Most of that change is water.

A Body Composition scale may attempt to make sense of this number. But try an experiment. Save up having to pee and weigh yourself before and after the pee. Record the water percentage before and after vs the weight. Your scale is probably not all that great at recording what you know is nothing but water weight.

Alcohol and Hydration

Alcohol consumption can affect hydration. I notice if I drink a fair amount one day that my weight goes down the next day. This has been studied (Alcohol. 2010 Jul-Aug;45(4):366-73. Hydration status and the diuretic action of a small dose of alcohol. Hobson RM1, Maughan RJ.).

Previous Day Exercise

Exercise can cause stress which causes the body to hang onto weight (I Just Started Exercising — Why Am I Gaining Weight?):

A new exercise regimen puts stress on your muscle fibers. This causes small micro tears, also known as micro trauma, and some inflammation. Those two conditions in your muscle fibers are the reason you may gain some weight. Your body responds to the micro tears and inflammation in two ways that cause temporary water weight gain. The first is a healing response.

“That stress and micro-tearing damage to the muscle fibers induces water retention in the body,” Dr. Calabrese explains. “There may be a small amount of inflammation around the micro tear, and your body retains fluid there to try to heal it.” These are short lived changes in the muscle.

The flip side is short term abstaining from exercising can cause water losses. Sunday is my off-day from exercise and I often see my weight drop on Monday mornings. This is a consistent pattern. Equally, Saturday workouts tend to be pretty intense and I often find myself going up on Sunday morning weigh-ins.

Don’t use this an excuse to not exercise. Just recognize that exercising can cause weight fluctuations.

Fecal Matter

There’s a delay between what we eat and what we poop. Clearly this leaves some weight in our bodies.

Glycogen Storage

When you fast overnight you are expending energy. And that energy comes largely from glycogen stores (at least more in the case of a carb burner). A fat burner (Low Carb diet person) gets more energy from fat but still has some glycogen stores.

Glycogen stores account for a very large amount of weight fluctuation. There are two reasons for this. Every gram of Glycogen is stored along with three or four grams of water held with Potassium (Glycogen Stores and Short Term Weight Loss).

The second reason is that the energy deficit required to reduce weight with glycogen as fuel is 1800 calories/lb which is less than the 3500 calories/lb for fat. So there’s a really big lever in this regard. It doesn’t take much energy to store water along with glycogen and it doesn’t take much energy to free water along with glycogen. Hence the two or three lbs you “lose” every night.

Are There Any Studies on Weighing?

There is an interesting study on weighing frequency (J Behav Med. 2017 Oct;40(5):846-853. Daily self-weighing and weight gain prevention: a longitudinal study of college-aged women. Rosenbaum DL, Espel HM, Butryn ML, Zhang F, Lowe MR.)? The study:

Daily self-weighing has been suggested as an important factor for weight loss maintenance among samples with obesity. This study is a secondary analysis that examined daily self-weighing in association with weight and body composition outcomes over 2 years among young women with vulnerability for weight gain.

Women (N = 294) of varying weight status completed self-weighing frequency questionnaires and weight was measured in the clinic at baseline, 6 months, 1, and 2 years; DXA scans were completed at baseline, 6 months and 2 years. Multilevel models examined the relationship between daily self-weighing (at any point in the study) and trajectories of BMI and body fat percentage.

Daily self-weighing was associated with significant declines in BMI and body fat percent over time. Future research is needed to examine causal relations between daily self-weighing and weight gain prevention. Nonetheless, these data extend the possibility that daily self-weighing may be important for prevention of unwanted weight gain.

What should be obvious is that it wasn’t the act of weighing that caused the loss of weight. IE, stepping on a scale probably didn’t cause the weight loss. It was the taking note of the weight on the scale that mattered.

It seems likely that these women who saw transient weight fluctuations interpreted these as an indication that they needed to reduce their caloric intake and decided to eat less. This seems like a self-corrective method. Those who didn’t weigh themselves didn’t know where they were and probably didn’t self-regulate. This was not a controlled trial and was limited to questionnaires about self weighing (an interesting PhD dissertation on self-weighing suggests some possibilities).

Weighing Strategy

If you were to eat at a 500 calorie a day deficit and all of that deficit was met from body fat (after glycogen stores are exhausted) then it would take a week to lose a pound (and there are some big assumptions here). So, even the strategy of weighing every week may not be helpful due to the fluxes from other sources noted above.

Could it might be a better strategy to record weight monthly? Weigh yourself daily and note the trends in your head but if you really want to see the direction check monthly.

Another strategy could be to fast around a particular weight. If you get above that weight then fast. That could work for some people. Make sure you have enough body fat to support a fast.


Author: Doug

I'm an Engineer who is also a science geek. I was pre-diabetic in 1996 and became a diabetic in 2003. I decided to figure out how to hack my diabetes and in 2016 found the ketogetic diet which reversed my diabetes.

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