Does carb loading right before a show make muscles look bigger?

Short answer

By 2–3% at most. Cutting carbs and then loading them raised muscle thickness by 2–3% and lifted photo scores. But 7 of 15 people who loaded in one go got diarrhea.

Does carb loading right before a show make muscles look bigger?
'Cut carbs → load carbs → full muscles' — does this formula hold?
A popular method says to slash carbs the week before a show, then pile them in over the last few days so muscles look full. We checked whether muscles actually get bigger and whether there is a cost.
How many people do it?
Only 6.2% of 81 competitors ate as usual
A survey of 81 competitors found that only 6.2% ate their normal diet in the week before the show. Adjusting carbs, water and salt were the most common methods. In a survey of 160 competitors, men ate about 490 g of carbs a day on their highest days that week.
What did the first experiment find?
Muscle girth did not grow in 9 people
In 1992, 9 people cut carbs to 10% of calories for 3 days, then loaded up to 80% for 3 days. Compared with the same training on a normal diet, there was no difference in arm, chest or thigh girth.
But what about muscle thickness?
Only the loaders got thicker, and photo scores rose
24 people were measured the day before a show. The 15 who loaded for 24 hours after 3 days of cutting gained arm muscle thickness and chest, arm and thigh girth, and their photo-based physique scores went up. The 9 who did not load showed no change.
How much bigger?
2–3% muscle thickness, less than 1 mm
In an experiment where 4 people took a carb drink and a fake drink in turns, muscle thickness rose 2.9% only on the carb days. The amount was about 630 g a day for a 70 kg (154 lb) person. That is like a 3 cm muscle getting 0.9 mm thicker.
Does the layer under the skin get thinner?
In 1 case, it shrank by 10%
1 person cut carbs for 3 days, then ate about 578 g a day for 2 days. Over that time, total muscle thickness rose about 1.6%, and by show day the layer under the skin was 10% thinner. This is the record of 1 person preparing for a show.
Is there a cost?
7 of 15 people who loaded in one go got diarrhea
Of the 15 who loaded within 24 hours, 7 got diarrhea, and 4 of them had it badly. During the low-carb days, constipation was common in both groups. In the 4-person experiment, responses differed from person to person, and the researchers advised testing the plan before the show.
Summary: muscles look bigger, by 2–3%
It is a final touch, not a transformation
Cutting and then loading carbs raised muscle thickness by 2–3% and lifted photo scores. The first experiment, which measured girth, found no difference, and 7 of 15 loaders got diarrhea. Trying the same plan in a practice run before the show and watching how your body responds works.