The truth behind the myth #15: "Deficiencies are always due to poor eating habits"

When a blood test reveals a deficiency or insufficiency, many people quickly jump to the same conclusion: their diet must be bad.

However, the reality is far more nuanced. While an unbalanced diet can indeed contribute to certain deficiencies, it is far from being the sole cause. The body's needs, its ability to absorb nutrients, lifestyle, and certain life stages also play a major role.

So, is a deficiency always synonymous with a poor diet?

Why is this myth so widespread?

The idea seems logical: since vitamins, minerals, and other nutrients come from our food, a deficiency must mean that our diet is unbalanced.

While this reasoning is sometimes true, it is far from summarizing the entire physiological reality.

Nutritional status depends on several parameters:

• dietary intake;
• individual needs;
• the body's ability to absorb nutrients;
• their storage;
• their utilization by different tissues.

A varied diet is essential, but it is not always enough to guarantee optimal intake for all nutrients.

What is truly meant by a deficiency?

A deficiency occurs when a nutrient is present in insufficient quantity to allow the normal functioning of the body.

Before a full deficiency, there is often a phase of insufficiency, during which reserves gradually decrease without causing obvious symptoms.

This is why some insufficiencies are only discovered during a biological assessment.

Eating a balanced diet doesn't always guarantee optimal nutritional status

Even with a generally balanced diet, certain situations can lead to insufficient intake or reduced availability of certain nutrients.

Several examples illustrate this:

• vitamin D is mainly synthesized through sun exposure;
• EPA and DHA omega-3s are primarily supplied by fatty fish, which are not widely consumed by part of the population;
• vegetarian or vegan individuals may have lower intakes of vitamin B12 or dietary creatine;
• some people consume few foods rich in magnesium or iron without necessarily having an unbalanced diet.

A balanced diet remains the foundation, but it does not always perfectly cover everyone's needs.

Needs that vary between individuals

We do not all have the same nutritional needs.

They can increase in various situations:

• intensive sports practice;
• growth;
• pregnancy and breastfeeding;
• aging;
• certain illnesses or periods of convalescence.

For athletes, for example, mineral losses due to perspiration can be greater, while energy and protein needs increase with training load.

Nutrient absorption also matters

Ingesting a nutrient does not automatically mean it will be properly absorbed.

Digestive absorption can be influenced by various factors:

• certain digestive pathologies;
• age;
• taking certain medications;
• interactions between nutrients.

For example, plant-based iron is generally less well absorbed than heme iron found in animal products. Conversely, vitamin C improves its absorption when they are consumed together.

Nutritional status therefore depends as much on what we eat as on what the body is able to use.

The most common deficiencies

Certain insufficiencies are particularly widespread in the general population.

The most frequent ones include:

• vitamin D, especially in winter or with low sun exposure;
• magnesium;
• EPA and DHA omega-3s;
• iron, particularly in women with heavy menstruation, pregnant women, or some endurance athletes.

The fact that they are common clearly shows that they do not only affect people with an unbalanced diet.

Are athletes more affected?

Yes, in some cases.

Training sometimes increases the needs or losses of certain nutrients.

For example:

• perspiration leads to losses of sodium, potassium, and magnesium;
• energy needs increase with training volume;
• certain endurance disciplines can increase the risk of iron deficiency;
• restrictive diets practiced to achieve a weight goal can reduce vitamin and mineral intake.

This does not mean that all athletes are deficient, but simply that they must be particularly attentive to their diet.

How to know if you are truly deficient?

The symptoms of a deficiency are often non-specific: fatigue, decreased energy, difficulty recovering, or reduced performance can have many causes.

Only a medical evaluation, possibly supplemented by biological analyses when relevant, can confirm a deficiency.

It is therefore preferable to avoid self-diagnosis or systematic supplementation without reason.

Do dietary supplements have a place?

Dietary supplements never replace a balanced diet.

However, they can be a relevant solution when needs are difficult to meet or when an insufficiency is identified.

For example, depending on the situation, certain supplements can help complement intake of:

• vitamin D;
• omega-3s;
• magnesium and other minerals;
• iron, only when recommended by a healthcare professional.

The goal is always to complement a quality diet, not to replace it.

Key takeaways

No, a deficiency is not necessarily a sign that you are eating poorly. It primarily reflects an imbalance between the body's needs, dietary intake, and the ability to utilize nutrients.

Needs vary according to age, physical activity level, lifestyle, and certain physiological situations. This is why two people with similar diets can have different nutritional statuses.

The best strategy remains to favor a varied and balanced diet, while keeping in mind that certain nutrients may sometimes require particular attention. When an insufficiency is confirmed or needs are increased, an appropriate dietary supplement can then find its place, in addition to a healthy lifestyle.