You're in a supermarket holding a cereal packet. It says 'low-fat' and the traffic light label is green showing that there's very little saturated fat. So far so good - for your waistline and your heart, right?
But then you notice that the sugar content is pretty high. So is a low-fat label really that healthy? The question has been going round in my head since reading an editorial in the BMJ this week that claims that saturated fat may not be the enemy it's been made out to be.
The editorial has stirred up one of the hottest topics about dietary advice this year. It asserts the opinion that saturated fat hasn't shown a risk to heart disease in several studies and may even be protective against some conditions. But recommendations about the amount of fat we should have in our diets haven't come out of thin air. The science behind them comes from a landmark study published in 1970. Researchers found that diets high in saturated fat were linked to higher levels of 'bad' cholesterol (low-density lipoprotein), which is a key risk factor for heart disease.
So, when it comes to protecting our health, which foods do we need to cut out or even eliminate? If saturated fat isn't the villain in our diets, what is? The editorial goes on to suggest that sugar and carbohydrates could be the key suspects.
The debate surrounding fats and sugars is fascinating and certainly food for thought. And it's sugar I want to focus on. It's been linked to weight gain, tooth decay and poor nutrition. That's nothing new. But in the last few years alone, evidence has been emerging to suggest sugar consumption is a key contributor to one of the biggest disease burdens of our modern world - type two diabetes.
In particular, there is mounting evidence to suggest that sugary drinks significantly increase the risk of this condition. The problem with a spoonful of sugar (or several in most fizzy drinks) is that it adds up to a lot of empty calories that can lead to weight gain. Furthermore, there's evidence to suggest that excessive amounts of sugar causes insulin resistance, which leads to type two diabetes.
To pull a few key stats, in a recent study, researchers found that drinking a can of sugar-sweetened soft drink increased the risk of type two diabetes in European men and women by 22%. Another piece of research found a 26% increased risk when people drank one or more sugary drinks per day compared with those who drank none or less than one a month. It seems sugary drinks have a lot to answer for.
Returning to the issue of weight loss, this leads me on to another key component of diet - carbohydrates. This energy-rich source of fuel has also been regarded as a culprit for weight gain in recent years. You only need to google 'low-carb diets' to be presented with over 17,000 results for ways you can jump start weight loss, curb cravings and burn more fat.
But thousands of results can't be wrong, can they? The effect of low carbs in your diet means that once your body uses up your stored glucose it then starts to burn stored fat instead. The concept of using fat for fuel has made these types of diets so appealing for people wanting to shift a few pounds.
The diet has divided opinion across the board, but for me there is definitely something in this sugary hypothesis. However, it isn't sustainable or healthy in the long term to substantially reduce carbs. Carbohydrates are vital for energy - they prevent protein being used for energy (as it's needed elsewhere), and helps keep your blood sugar levels on an even keel. These are the 'good' carbs.
So perhaps it's more to do with a re-education about carbohydrates - because some carbs can be bad for you. Refined, processed carbs, such as white bread, fast food burgers and white pasta contain sugars that are easy to digest and strip away beneficial fibre. And it's these 'sugar' carbs that can lead to weight gain. Found in thousands of food products - it's no wonder they've been touted as 'fat foods'.
So where does this leave us? The food fight against long-term conditions such as obesity, cardiovascular disease and type two diabetes is an absolutely crucial one - one we are currently losing.
When it comes to reducing the risk of these conditions, the food we put into our bodies is something each and every one of us is responsible for. Yet individual responsibility is not enough: indeed there is some evidence that obesity is partly mediated through an addictive process. It's therefore imperative that scientists, policy makers and governments also empower individuals to make behavioural changes happen on a large scale. The advice we give about food and diet is as powerful as any medicine - it can do significant harm if we don't get it right.