Constipation During a Diet or Cut: Why It Happens and How to Fix It

Constipation during a caloric deficit is nearly universal. People assume it's a sign that something is wrong with the diet format. Usually, it isn't � it's a predictable mechanical consequence of reducing one specific thing.

Why Cutting Carbohydrates Causes Constipation

To lose fat, you need a caloric deficit and controlled insulin levels. The most effective way to lower insulin is to reduce carbohydrates.

The problem: most complex carbohydrates � oats, buckwheat, pearl barley, legumes � have a low glycemic index specifically because they contain substantial dietary fiber. When you reduce carbohydrates, you also reduce fiber intake proportionally.

Dietary fiber serves two physical functions in digestion:

• Insoluble fiber stimulates intestinal peristalsis � the mechanical movement of contents along the digestive tract. Less fiber = weaker peristaltic stimulus = slower transit = constipation.
• Soluble fiber absorbs water, forms gel, and increases the mass and softness of intestinal contents. Less fiber = smaller, harder stools.

Neither of these effects is about what you're eating � they're about what's physically present in the intestinal lumen to provide volume and mechanical stimulus.

The Fix

Add fiber back explicitly, separately from carbohydrate intake:

Soluble fiber supplements � psyllium husk (available as Mucofalk at pharmacies, or cheaper in bulk form) swells significantly in water and is highly effective at resolving constipation mechanically. Minimum 2 tablespoons per 350-400ml of water. Drink additional water throughout the day.

Low-glycemic fiber vegetables � broccoli, green beans, string beans, leaf vegetables. These contain fiber without meaningful carbohydrate impact on insulin. Increasing them alongside a reduced-carb diet maintains fiber intake without reintroducing high-glycemic carbohydrates.

Water intake � fat metabolism produces metabolic waste products that require water for excretion. During a cut, water requirements increase. Inadequate water directly worsens constipation.

The Target

Regular bowel movements � at least once per day, ideally twice � should be maintained throughout a cut or diet. This is the practical indicator that fiber and water intake are adequate.

The exception: final days before a competition with deliberate water depletion. That's a separate protocol with different goals and different rules, not applicable to general fat loss.

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