Can your gut issues be the result of sub-optimal nutrition?

Digestive symptoms have become so common that many people now view bloating, reflux, constipation, diarrhoea and abdominal discomfort as an unavoidable part of daily life. In many of my clients, these symptoms are not driven by "food intolerances", but rather a lifetime of sub-optimal nutrition and in some individuals, outside malnutrition.

In modern societies, malnutrition rarely looks like starvation. Instead, it presents as diets that provide enough – or even excessive – calories, while failing to supply the full range of nutrients required for healthy digestion, gut barrier integrity and microbial balance. This form of malnutrition is increasingly common and frequently overlooked.

In addition, there are many diets being promoted stating that they will "fix" your health issues, ranging from low-carbohydrate, ketogenic, carnivore, low-fat, plant-based, vegan, paleo, intermittent fasting, time-restricted eating, juice cleanses, detox programmes, elimination diet and the ever-evolving "biohacking" approaches that are growing in popularity. Almost daily, a new dietary trend promises improved digestion, weight loss, metabolic health or symptom relief through restriction, removal, or inflexible rule.

Why consistency matters more than extremes

Digestive health is supported by nutritional adequacy and consistency, not dietary extremes. Highly restrictive eating patterns may offer short-term symptom relief, but often at the expense of long-term gut resilience and nutrient sufficiency.

The gut thrives on predictable fuel, diverse plant intake and balanced macronutrients.  When these foundations are missing, malnutrition can develop quietly, driving symptoms that are frequently misattributed to intolerance or stress alone. 

While some of these approaches may offer short-term benefits for certain individuals, many unintentionally create nutritional gaps. Over time, this can lead to malnutrition driven by sub-optimal nutrition, particularly when entire food groups are excluded. 

Malnutrition in a world of plenty

Ultra-processed foods, restrictive dieting trends and inconsistent eating patterns have created an environment where energy intake is high, yet nutrient density is low [1].  People may eat regularly, follow popular dietary frameworks and still experience functional malnutrition, particularly at the level of micronutrients, fibre and bioactive plant compounds.

This type of malnutrition is rarely identified through routine blood tests and often goes untreated, despite its strong association with digestive complaints, immune dysregulation and altered gut microbiome.

The gut is a high-demand organ system. It requires continuous nutritional input to repair its lining, regulate immune activity, produce digestive enzymes and support the trillions of microbes that contribute to digestion and metabolic health. When nutrition falls short, gut function is often the first system to reflect the imbalance.

Macronutrients: The foundations of digestive health

Carbohydrates, fats and protein are often portrayed as dietary adversaries rather than collaborators. However, removing or severely restricting any macronutrient increases the risk of malnutrition, particularly when done long-term. 

Protein and gut repair

Protein [2] provides the amino acids required for:

• renewal of the intestinal lining
• production of digestive enzymes
• immune signalling molecules
• neurotransmitter synthesis within the gut-brain axis

Inadequate protein intake compromises gut repair and increases vulnerability to inflammation. This is especially relevant during ageing, periods of stress and chronic illness. While needs vary between individuals, consistent protein intake from diverse sources is essential for preventing nutrition-related gut dysfunction.

Protein-rich foods do not need to be excessive or expensive and include poultry, eggs, legumes, tofu, tempeh and cruciferous vegetables. 

Carbohydrates, fibre and the microbiome

Carbohydrates are frequently blamed for digestive symptoms, yet the issue is rarely carbohydrates themselves, but rather the absence of fibre-rich, complex carbohydrate sources.

Dietary fibre [3] plays a central role in gut health by:

• supporting bowel motility
• feeding beneficial gut bacteria
• promoting short-chain fatty acid production
• reducing gut inflammation

Low fibre diets are a major contributor to gut-related malnutrition. Without sufficient fibre, microbial diversity declines, fermentation capacity weakens, and gut barrier function deteriorates. This can lead to bloating, irregular stools and increased sensitivity to foods.

Whole grains, vegetables, legumes, fruits and root vegetables remain foundational for digestive resilience.

Dietary fat and nutrient absorption

Dietary fat is essential for the absorption of fat-soluble vitamins A, D, E and K. When fat intake is chronically low, secondary malnutrition can develop even when overall food intake appears adequate.

Unsaturated fats support:

• anti-inflammatory signaling
• cell membrane integrity
• hormone production
• brain-gut communication

Polyunsaturated fats, particularly omega-3 fatty acids [4], are required from the diet and have been shown to support gut microbial balance and reduce inflammatory signalling in the gastrointestinal tract. 

Micronutrients: The silent drivers of gut function

Micronutrient malnutrition is one of the most under-recognised contributors to digestive dysfunction. Deficiencies may develop gradually and co-exist with otherwise "healthy" eating patterns.

Commonly insufficient nutrients include:

• zinc, essential for gut barrier integrity [5]
• magnesium, critical for gut motility and nervous system signalling
• vitamin D, involved in immune regulation and intestinal permeability
• B vitamins, required for epithelial renewal and energy metabolism
• iron, selenium, supporting cellular energy and antioxidant protection

Even mild deficiencies can impair digestion, alter microbial composition and reduce the gut's capacity to repair itself.

Fibre and polyphenols: Feeding the gut ecosystem

The gut microbiome depends on nutrients that humans cannot digest. Fibre and polyphenols reach the colon intact, where they are metabolised by microbes into compounds that regulate inflammation, immunity and gut barrier strength.

Key fibre types include:

• inulin
• resistant starch
• beta-glucans
• pectins

Polyphenols, found in foods such as berries, olive oil, cocoa, coffee, tea, herb and seeds, act as selective microbial modulators. Diets low in these compounds are strongly associated with diet-related malnutrition and reduced microbial diversity. 

Reframing gut health and malnutrition

Malnutrition doesn't always present itself as weight loss or visible illness. It often exists beneath the surface, shaping digestion, immunity and microbial health over time. 

If you’ve been struggling with digestive symptoms despite trying different diets or intolerance testing, it may be time to take a deeper look at your gut health. Reach out to a nutritional professional to start your journey.

References

1. Mansour SR et al (2021). Impact of diet on human gut microbiome and disease risk. New Microbes New Infect. 2021 Feb 2;41:100845. doi: 10.1016/j.nmni.2021.100845. PMID: 34035924; PMCID: PMC8138677.
2. Beaumont M, Blachier F. Amino Acids in Intestinal Physiology and Health. Adv Exp Med Biol. 2020;1265:1-20. doi: 10.1007/978-3-030-45328-2_1. PMID: 32761567.
3. Kay RM. Dietary fiber. J Lipid Res. 1982 Feb;23(2):221-42. PMID: 6281350.
4. Zou B et al (2025). Insight into the effects of Omega-3 fatty acids on gut microbiota: impact of a balanced tissue Omega-6/Omega-3 ratio. Front Nutr. 2025 May 16;12:1575323. doi: 10.3389/fnut.2025.1575323. PMID: 40453723; PMCID: PMC12124128.
5. Islam T et al (2023). Anti-inflammatory mechanisms of polyphenols in adipose tissue: role of gut microbiota, intestinal barrier integrity and zinc homeostasis. J Nutr Biochem. 2023 May;115:109242. doi: 10.1016/j.jnutbio.2022.109242. Epub 2022 Nov 26. PMID: 36442715.