Found in many “low-sugar” or “keto” bars, sugar alcohols such as Maltitol, Erythritol, Xylitol, Sorbitol, or Isomalt are synthetic sweeteners used to mimic sugar’s taste and texture. They’re incompletely absorbed in the small intestine, and what remains ferments in the colon, often causing gas, bloating, or diarrhea, especially in sensitive individuals. Their osmotic effect draws water into the gut, intensifying these symptoms at higher doses. Some studies suggest they may also trigger appetite rebound, as sweetness without calories can confuse the body’s hunger signals. While they help products appear “low-sugar,” sugar alcohols are ultra-processed starch derivatives that often undermine digestive comfort.

An ultra-processed starch derivative made from industrial corn — often GMO and pesticide-treated — and marketed as soluble or maize fiber. It’s used to inflate fiber numbers and lower net carbs, even though most versions are only partially resistant, meaning your body still digests much of it like regular carbs. It adds bulk and chew but offers little prebiotic benefit and can cause gas or bloating in many people. Despite the wholesome name, it’s a filler ingredient with more marketing value than nutritional value.Found in countless “low-net-carb” bars.

Cheap, synthetic filler made by heating corn sugar. Commonly used in protein bars to inflate “fiber” content and reduce net carbs — without providing real nutritional value. While it’s legally classified as a soluble fiber, it’s not prebiotic and doesn’t nourish beneficial gut bacteria like resistant dextrin does. It also ferments unpredictably in the colon, often leading to bloating or other GI discomfort. Found in many “high-fiber” bars.

Synthetic compounds made from petroleum-derived chemicals to imitate real foods like vanilla or chocolate. Because they’re protected as trade secrets, brands don’t have to list their contents — which can include solvents, preservatives and carriers linked to sensitivities or headaches in some people. Found in the majority of protein bars.

Cheap, industrial fats extracted from crops like palm, soybean, sunflower, or canola — often refined, bleached, and deodorized under high heat. Used in bars to replace costly cocoa butter and improve texture at a fraction of the price. Most are derived from GMO or pesticide-heavy crops and are rich in omega-6 fatty acids, which can promote inflammation when consumed in excess. These oils are also unstable when heated, forming oxidized byproducts that degrade quality over time. Palm oil in particular raises environmental and ethical concerns, linked to deforestation and habitat loss. Found in many mainstream protein or energy bars.

Lower-grade protein containing a mix of protein, fat and lactose. It’s far less pure than isolate and is often used in bars to cut costs while still allowing “high-protein” claims on the label. Because it’s less refined, it can contain oxidized fats, denatured proteins and residual lactose, which may cause bloating or digestive discomfort in sensitive individuals. Whey Protein Concentrate (WPC) also mixes poorly, has a shorter shelf life and can carry an off-milky taste that’s masked with heavy flavoring or sweeteners. Found in many mass-market “high-protein” bars.

Common low-cost protein bases used to bulk up bars and shakes. While they sound natural, both are heavily processed isolates that often come from GMO or pesticide-treated crops. Soy in particular is one of the most sprayed crops in the U.S., and unless it’s organic or non-GMO, trace residues may remain. Non-organic soy isolates are typically extracted using hexane, a petroleum-based solvent. Some soy ingredients also contain phytoestrogens (isoflavones) that can mimic estrogen in the body and may disrupt hormones in sensitive individuals or young children. Pea protein can carry residual anti-nutrients that impair mineral absorption and is harder to digest than dairy proteins. Both are highly refined plant isolates with questionable purity and limited amino-acid completeness compared to milk-derived protein. Found in most "plant-based” or vegan bars.

Additives like guar gum, xanthan gum, carrageenan or cellulose gel are used to bind ingredients, add chewiness and mimic creaminess without real fats or fiber. They’re cheap bulking agents that improve texture and shelf stability — not nutrition. In larger amounts, these compounds can trap gas and water in the gut, leading to bloating, cramping, or irregular digestion, especially in sensitive individuals. Some (like carrageenan) have been linked to gut irritation and low-grade inflammation in animal studies.

A sticky plant protein found in wheat, barley, and rye — prized in manufacturing for its binding and chewy texture. In protein bars, it’s often added through wheat protein isolate or hydrolyzed wheat flour to lower cost and boost protein numbers. For many people, gluten can cause bloating, inflammation or fatigue, even without full celiac disease. It’s also one of the most common food sensitivities, linked to gut irritation and reduced nutrient absorption in sensitive individuals.