Why You Shouldn't Eat 5 Portions

The public is completely unaware that the strength of the message is not matched by the strength of the evidence. DR BARNETT KRAMER

Some time ago I was making a documentary video. The then-current craze for low-carb diets, sparked by a sudden upsurge in the Atkins diet, was causing all kinds of confusion. The idea of the documentary was to sort out the truth from the hype and, hopefully, give some useful advice.

We interviewed several dieters about their experiences on various slimming regimes; they reported on the benefits of low-carb, high-fat diets. But wanting to be unbiased and put both sides of the debate, we also interviewed three general medical practitioners and three nutritionists / dieticians.

One of the dieticians, I’ll call her Jane, came to be interviewed directly from the British Dietetic Association (BDA) headquarters in London. During the interview, I asked Jane why the BDA recommended five portions of fruit and vegetables a day. ‘Because that’s healthy eating,’ she told me. ‘Yes’, I said, ‘but what is the basis for the recommendation – the evidence?’ Jane told me that it was government advice. ‘But,’ I persisted, ‘that isn’t evidence.’ I asked again on what evidence the recommendations were based: Which study or studies had shown that ‘five portions’ was healthy?’ ‘It’s healthy eating’, she replied. I didn’t continue: it was obvious that we were going to get nowhere; that she had no idea why she recommended five portions.

I tried another tack. The BDA and American Dietetic Association base their recommendations on The Framingham Heart Study. I knew that this study had been misrepresented so I decided to ask for her comments on the various pronouncements from Framingham that did not agree with the BDA’s recommendations (see Chapter ??). I started by asking: ‘Would you agree with me that the Framingham Study is the world’s most respected study into the dietary causes of heart disease?’

‘What’s the Framingham Study?’ she asked. Well, that stopped me in my tracks and, although I did ask further questions, it effectively finished the interview.

Jane was paid her £150 fee and left. A week later her cheque was returned with a letter from her solicitor warning us that action would be taken if we used any part of her interview in the video.

Jane’s was not an isolated case. In the end, although we used material from all the doctors, we couldn’t in all conscience use material from any of the nutritionists / dieticians without compromising their careers. It was obvious even to the camera crew that none of them knew their subject.

The science is flawed

It’s not difficult to see that the science behind the ‘5 portions’ recommendations is flawed if you compare the portion sizes as defined by US and UK governments, which show wide discrepancies. If the recommendations were made on the basis of a rational analysis of a coherent body of data then one would expect the recommendations on both sides of the Atlantic to be similar. But they aren’t. Below is a comparison of official US[1] and UK[2] advice. First, the numbers of portions and their sizes:

Table I: Comparison of US and UK ‘5 portions’ recommendations

Serving sizes	USA	UK	US : UK Ratio
Fruits or vegetables	8tbs (1/2cup)	3tbs	2.67 : 1
Whole fruit	One medium-size fruit	One medium-size fruit	1 : 1
Fruit juice	3/4 cup (6 fl oz.)	'one small glass 150ml'* (approx 5 fl oz.) †	1.2 : 1
Canned or frozen legumes	8tbs (1/2 cup)	Unclear ††	?
Raw, leafy vegetables	16tbs (1 cup)	1 cereal bowl (However much this is)	?
Dried fruit	4tbs (1/4 cup)	Unclear – but '1 heaped tbs'*	4? : 1

* (http://www.bbc.co.uk/health/healthy_living/nutrition/dietary_cvd.shtml)
† only one portion per day counts
†† although no portion size is given, extra portions don’t count.

You can see from the above table that a portion size can vary dramatically between the US and UK. Also, in the UK, dietary components such as fruit juice, legumes and dried fruit only work their magic on the first portion, as extra portions are not counted as far as the ‘5 portions’ rule is concerned. In the US it all counts. Another anomaly is that, in the USA, raw vegetables count just as much as cooked ones, even though the bioavailability of the nutrients in raw vegetables is much lower than in cooked vegetables.

Supposed benefits

The two countries also claim different benefits from eating ‘5 portions’. The American Dietetic Association says:

‘Research has shown that eating 5 A Day reduces the risk of cancer, heart disease, stroke, diabetes, and other diseases. Cancer, heart disease, and stroke are the three leading causes of death in this country. People who eat 5 A Day have a third of the risk of developing cancer as those who eat only 1-2 servings a day. In fact, eating a diet rich in fruits and vegetables could prevent more than 20 percent of cancer deaths each year.’
‘It’s hard to go wrong if you fortify your diet with colourful foods. Almost every one of them is loaded with disease-proofing compounds.’

While, here in Britain, we are told simply that:

‘The Government recommends an intake of at least five portions of fruit or vegetables per person per day to help reduce the risk of some cancers, heart disease and many other chronic conditions.’

Last updated 7 April 2010