“Eating junk food has a negative effect on mental health, making those who consume it regularly feel depressed,” said The Daily Telegraph.

The news is based on a Spanish study that looked at how 9,000 people’s consumption of fast food and baked goods, such as pies and pastries, related to their risk of depression. In a week when tax on pasties and pies has been the source of great distress for some, researchers found that people who consumed the most fast food and baked good were 37% more likely to become depressed over a six-year period than people with the lowest consumption.

This study had some strengths. For example, it established people’s diets before they were followed to see if they developed depression, which means their diets preceded their depression. However, it cannot conclusively show that fast food directly causes depression. For example, it is just as plausible that diet and depression are both the result of a common factor. Therefore, it’s too early to rebrand the burger and fries as an “unhappy meal”.

Where did the story come from?

This Spanish study was carried out by researchers from the University of Las Palmas in Gran Canaria and the University of Navarra. It was funded by the Spanish Government’s Carlos III Institute of Health.

The study was published in the peer-reviewed journal Public Health Nutrition.

The study’s methods were covered appropriately by the media. However, the 51% increase in risk of depression that was quoted by the Telegraph and Daily Mail did not appear in the research paper. The paper reported an increased risk of 37%.

What kind of research was this?

This prospective cohort study assessed the relationship between eating fast food or processed pastries and developing clinical depression. The research project, called Seguimiento Universidad de Navarra (SUN), is a long-running cohort study that involves university graduates in Spain. The study continuously recruits new participants, and collects data on a variety of factors using mailed questionnaires.

Prospective cohort studies assess participants and then look at the development of various factors over time. They have the advantage of initially measuring the exposure of interest (in this case, consumption of fast foods or processed pastries) in a group of people who do not already have the outcome of interest (in this case, clinical depression). This allows the researchers to be certain that the exposure came before the outcome, which is important for determining a cause-and-effect relationship.

Cohort studies can collect data on a number of other factors that may also account for the relationship between the exposure and outcome. These factors are known as confounders. Adjusting their results to account for the influence of confounders allows researchers to be fairly certain that these confounding factors do not influence the results. However, they cannot take into account factors that weren’t measured during the study. Therefore, it is possible that, during a cohort study, unknown factors may account for the relationship seen, rather than the exposure of interest.

What did the research involve?

The researchers used data from the SUN study to identify participants for their research. They included people who did not have a clinical diagnosis of depression and who were not taking antidepressant medication (to ensure that the participants were free of depression at the beginning of the study). All participants were also free of cardiovascular disease, diabetes and hypertension.

The participants completed the food frequency questionnaire at the beginning of the study. They assessed two exposure variables: fast food consumption (which included hamburgers, sausages and pizza) and consumption of commercial baked goods (which included muffins, doughnuts, croissants and other baked goods). The researchers then divided the cohort into five groups (quintiles), based on the amount of each food group that they usually consumed.

The participants were then followed up for a median of 6.2 years. The researchers used a mailed questionnaire to determine whether the person had been diagnosed with clinical depression or had been prescribed antidepressant medication during this time.

The researchers collected data on other variables they thought might influence the relationship between eating habits and depression. These included age, sex, body mass index, smoking status, physical activity level, total energy intake and healthy food consumption. They then adjusted for the influence of these variables during the statistical analysis.

What were the basic results?

In total, 8,964 participants were included in the study. Participants with the highest consumption (quintile 5) of fast food and baked goods were more likely to be single, younger, less active and have worse dietary habits than participants with the lowest consumption (quintile 1).

After a median follow-up of 6.2 years, 493 cases of clinical depression were reported.

When assessing the relationship between fast food consumption and the development of depression, the researchers found:

• There were 97 cases of depression in the group with the lowest consumption (quintile 1) compared with 118 cases in the group with the highest consumption (quintile 5). When the sizes of the quintiles were taken into account, this equated to people with the highest levels of consumption having a 37% greater risk of developing depression than those with the lowest levels of consumption (hazard ratio [HR] 1.37, 95% confidence interval [CI] 1.01 to 1.85).
• Intermediate levels of consumption (quintiles 2, 3 or 4) were not associated with significantly increased risk of developing depression compared to the lowest consumption level.

When assessing the relationship between commercial pastry consumption and the development of depression, the researchers found:

• People with the highest level of consumption (quintile 5) had a 37% increased risk of developing depression compared to the lowest consumption group (quintile 1) (HR 1.37, 95% CI 1.01 to 1.85).

How did the researchers interpret the results?

The researchers concluded that their results demonstrate “a positive dose-response relationship between the consumption of fast food and the risk of depression”. In other words, as consumption of fast food increases, so does the risk of depression. They also said that “consumption of commercial baked goods was also positively associated to depressive disorders.”

Conclusion

This study has found an association between consuming high levels of fast food and baked goods and the risk of developing depression. Even though this was a prospective study, it cannot conclusively show that eating lots of hamburgers, sausages and pizza causes depression. The tendency to consume fast food and develop depression may both have stemmed from some common factor, rather than fast food directly causing depression. For example, participants with the highest fast food consumption were generally all single, younger and less active, which may have influenced both their diet and their risk of depression.

Several important factors should be noted:

• This study used a questionnaire to determine whether a person had clinical depression. This method may be less reliable than either a clinical interview or a diagnosis confirmed by medical records. Some people with depression may not have reported that they had been given a diagnosis. Alternatively, other people may have considered themselves to have depression without having a clinical diagnosis from a doctor. Equally, some people who would have met diagnostic criteria for depression had they seen a doctor may not have realised that they had the condition.
• Though the researchers adjusted their results for lifestyle and socioeconomic factors that may have influenced diet and depression risk (potentially confounding the relationship between the two), depression may be triggered by many factors. It is difficult to ensure that all possible confounders were taken into account.
• If there is a direct association between these dietary items and risk of depression, the underlying mechanism by which eating these foods could lead to depression is not known.
• The cohort excluded people with multiple underlying illnesses and conditions, such as cardiovascular disease and high blood pressure. While this allowed the researcher to ensure these conditions did not influence their results, it makes it difficult to generalise the results to the wider population. Also, these types of illnesses may influence both diet and risk of depression, so it is arguable that including people with them could have been a valid option.
• The cohort was divided into groups based on their relative consumption of fast foods and commercial baked goods, and not on an absolute level of consumption. Therefore, the results of this study would only apply to a population that had a similar pattern of consumption.

Overall, this study suggests that there may be an association between eating a lot of fast food or baked goods and developing depression. It is, however, difficult to apply the findings to other groups of people, and it is unclear if the relationship would remain under different conditions.

Some takeaway pizzas are saltier than the Atlantic Ocean, say health campaigners concerned about the amount of salt we eat. Several newspapers have reported on the high levels of salt in pizzas from both takeaway outlets and supermarkets. Some of the pizzas contained more than 10g of salt, which is more than an entire day’s salt allowance.

An analysis of 199 pizzas by the Consensus Action on Salt & Health (CASH) group found no low-salt options, with over half the takeaway pizzas containing more than 6g of salt – the recommended daily maximum for healthy adults. Shop-bought pizzas generally fared better, but many still contained more than 5g of salt – close to the daily maximum allowance.

Keeping track of how much salt we eat is important as salt can raise blood pressure, in turn raising the risk of problems such as heart attacks and strokes. Many pizzas were also found to be high in fat and saturated fat, again marking them out as an unhealthy option.

Where has the news come from?

The action group CASH is concerned about the amount of salt we eat and its impact on our health. The group comprises academics, physicians and public health experts. CASH recently conducted a survey that examined the amount of salt in pizzas available throughout London. They included 199 margherita and pepperoni pizzas from takeaways, chain restaurants and supermarkets in their study. The CASH report included information on the amount of salt per 100g of food, as well as the amount of saturated fat contained in the pizzas.

How much salt should I eat?

CASH and NHS Choices recommend that adults consume a maximum of 6g of salt a day (approximately one full teaspoon). However, UK adults currently consume an average of 8.6g a day. The recommended maximum daily levels of salt for children are:

• under 1 year old – less than 1g
• 1 to 3 years old – 2g
• 4 to 6 years old – 3g
• 5 to 10 years old – 5g
• 11 years and older – 6g

It is important to limit salt intake as it affects blood pressure and, in turn, the risk of serious health problems such as strokes and heart attacks. CASH estimates that if the nation reduced its intake to recommended levels, it could reduce the number of strokes by 22% and heart attacks by 16%.

Which were the saltiest takeaways?

The CASH survey found that the top five saltiest takeaway pizzas were:

• Adam & Eve pepperoni pizza in Barnet – 2.73g of salt per 100g of food, equivalent to 10.57g of salt in their 388g pizza
• La Vera Italia pepperoni pizza in Wandsworth – 2.43g of salt per 100g of food, or 10.68g of salt per 439.6g pizza
• Ciao Bella pepperoni pizza in Havering – 2.21g of salt per 100g of food, or 9.22g of salt per 417.4g pizza
• Ciao Bella margherita pizza in Havering – 2.13g of salt per 100g of food, or 7.69g of salt per 361.8g pizza
• Il Mascal Zone pepperoni pizza in Barnet – 2.08g of salt per 100g of food, or 9.21g of salt per 442g pizza

The CASH survey found that more than half of all takeaway pizzas surveyed contained over the recommended maximum of 6g of salt a day. CASH points out that makers of takeaway pizzas do not have to provide nutritional information, which can make it difficult to know how much salt you are consuming.

Which were the saltiest shop-bought pizzas?

The CASH survey found that the top five saltiest shop-bought pizzas were:

• Tesco full-on-flavour simply pepperoni thin stonebaked pizza (fresh) – 1.8g of salt per 100g of food, equivalent to 4.77g of salt in their 265g pizza
• Iceland stonebaked spicy double pepperoni pizza (frozen) – 1.7g of salt per 100g of food, or 6.29g of salt per 370g pizza
• Morrisons extra thin triple pepperoni pizza (frozen) – 1.7g of salt per 100g of food, or 5.81g of salt per 342g pizza
• Dr. Oetker ristorante pizza pepperoni salame (frozen) – 1.68g of salt per 100g of food, or 5.36g of salt per 320g pizza
• Dr. Oetker Casa di Mama pizza quattro formaggi (frozen) – 1.6g of salt per 100g of food, or 6.32g per 395g pizza

Overall, the CASH survey found that 85% of shop-bought pizzas provided nutritional information on the front of the packaging, which may make it easier for customers to choose lower-salt options.

Were there any low-salt options?

Among the 199 shop-bought and takeaway pizzas, CASH did not identify any low-salt options (defined as 0.3g of salt or less per 100g of pizza).

There were, however, several medium-salt options (defined as 0.3-1.5g of salt per 100g). The takeaway with the lowest salt content pizza was Trattoria Pizzeria’s margherita pizza, with 0.778g of salt per 100g of food, equivalent to 2.15g of salt in their 275.8g pizza. However, this pizza contained a high amount of saturated fat.

The lowest salt content in a supermarket pizza was found in the ASDA Chosen by You cheese and tomato pizza, which contained 0.6g salt per 100g of food, equivalent to 0.64g of salt in the 106g pizza. This pizza also had medium levels of saturated fat.

How were the tests performed?

The survey looked at both pepperoni and margherita pizzas available in takeaways in 17 London boroughs and 8 supermarkets. They included 81 takeaway pizzas and 118 supermarket pizzas.

At present, companies selling takeaway pizzas are not required to publish nutritional information such as salt and fat content, so researchers took samples of each pizza and sent them away for lab analysis. They were analysed for the amounts of fat, saturated fat, sodium and calories per 100g. Researchers also recorded the total weight of the pizza, as well as diameter and pepperoni weight.

Supermarket pizzas are required to provide nutritional information on the packaging. For the 118 pizzas in this group, CASH photographed the packages, recording the salt, sodium, calories, fat and saturated fat content per 100g of pizza, as well as whether or not the packaging included a nutritional label on the front, the package weight and the portion weight.

How can I make a low-salt pizza?

CASH says that one way to reduce your daily salt intake and avoid the hidden salt found in many ready-made foods is to make your own pizza. CASH provides the following low-salt, low-fat recipe:

Serves: 2 (1 pizza) Preparation time: 15-20 minutes plus 1 hour rising time Cooking time: 30-40 minutes

For the base 300g strong white bread flour, plus extra for rolling out ½ teaspoon (half a 7g sachet) fast-action yeast Pinch of ground black pepper 100ml warm water 1 tablespoon olive oil, plus extra for greasing 1 garlic clove, crushed

For the sauce ½ teaspoon olive oil 1 small onion, chopped 1 garlic clove, finely chopped 1 tablespoon tomato purée 1 x 227g tin chopped tomatoes Pinch of chilli flakes, or to taste Freshly ground black pepper, to taste Handful of fresh basil, roughly chopped

For the topping 1 yellow pepper, sliced 1 tomato, sliced 100g cooked chicken 2 tablespoons sweetcorn 60g mozzarella, thinly sliced A few basil leaves, torn, plus extra to garnish

1. To make the dough, mix the flour, yeast and black pepper together in a large bowl. In a separate container, mix the water with the oil and garlic and pour into the flour and yeast. Mix together quickly with a spoon until a sticky dough is formed. Leave to stand for 10 minutes.
2. Dust your hands and a work surface with flour. To knead the dough, hold one side of the dough down with one hand and, with the other hand, push the other side of the dough away from you, stretching it out. Fold the stretched dough back on top of itself and push it down with your palm. Give the dough a quarter turn and repeat the process for just one minute or until the dough is smooth, elastic and bouncy.
3. Form a ball with the dough and place it into a bowl greased with a little oil. Cover the bowl with cling film and leave to rise in a warm place for about an hour or until the dough has doubled in size.
4. Meanwhile, make the sauce. Heat the oil in a saucepan over a medium heat and cook the onion and garlic for 5 minutes or until the onion becomes soft and transparent. Stir in the tomato purée followed by the chopped tomatoes, chilli and pepper. Simmer on a low heat for 15-20 minutes until the sauce becomes thick. Stir in the basil for the last few minutes. Use a hand blender to make a smooth sauce.
5. Once the dough has risen, preheat the oven to 240°C/475°F/gas 9. Dust a baking sheet with a little flour and use your hands to push the dough outwards to form a round base approximately 30cm (12 inches) across.
6. Spread the tomato sauce over the pizza base using the back of a spoon. Scatter the toppings over the pizza, top with the basil leaves and cook in the oven for 10-15 minutes or until golden brown. Scatter the remaining basil leaves on top and serve.