Couldn't find the booklet I had in relative nutritional values but I found this PDF. It discusses the Historical Changes in the Mineral Content of Fruit and Veg grown 50 years apart. Document appears to be from 1997.
http://www.google.co.uk/url?sa=t&source=web&cd=7&ved=2ahUKEwjKp_yVi7XZAhVIK1AKHQVSCosQFjAGegQICRAB&url=https://pdfs.semanticscholar.org/4612/520834c1043b76e1f475cedfdba5a208ef3a.pdf&usg=AOvVaw2rcj8W7oldUv2QxtmLK9nk
The conclusion seems to be a significant reduction in both fruit and veg and veg of various minerals.
The main table showing the differences is on page 3.
Sorry Just got around to properly reading this.
It's at this point I have to admit to owning not one but two copies of the mentioned "composition of foods" How sad I'm I ?
these tables of data are the basis for most of the calculated nutritional labelling for food in the UK (equivalent to USDA in America), although nowadays retailers insist that anything associated with a claim, or that is processed and prone to natural batch to batch variability is also independently analysed to confirm the figures. You then have to show a history of analysis for each product and amend the product composition labelling if these change significantly over time (due to change of supply of ingredients, tweaks to process etc).
Most of the time manufacturers use the analytical figures and sense check against the theoretical. This is partly because the composition varies so much but also because processing changes some heat labile vitamins and has a concentrating\diluting effect (driving off and injecting water with steam). Theres more to it than that but those are two things that can happen from many. Theoretical book values are mainly used on things like produce that has minimal processing (eggs, nuts, raw meat, fruit and veg).
The two copies I have are 15 years apart in terms of updates and both a lot newer than the data used in the study. These figures aren't static and are updated every 15 years. I think it would be interesting to look through the two versions I have of "the composition of foods" and compare some of the fresh produce to her older versions ...but so far I haven't been quite that interested
She annoyed me anyway but not tabling the difference and P value per item. I noticed for example that many went up over time. Magnesium was lower on a few items but up on others which is interesting in itself. However most of the fruits and vegetables she looked at are not particularly good sources of magnesium anyway.
The latest version of the tables I have, incorporated a new method for the determination of fibre. This change to fibre also changed some of the other figures significantly (e.g. Carbohydrates). Some of these method changes over the years have changed the data significantly. When I used to analyse fats for example in the 1980s this involved a completely time consuming method that lasted days. However this was an advanced method at the time compared to the 1930's and 60's. Nowadays we have rapid methods for most of the key nutritional table. It stands to reason that newer methods sometimes uncover previously reported errors (the fact that some of the figures in the paper go up and down sort of suggests the difference may be due to this....really needs more analysis!). I am not convinced that what she is looking at isn't just method related and I don't think she answers this properly in her discussion. We have a reference to this ... Popeye and spinach ...this was actually based on an embarrassing error that lead to it being wrongly reported as being 10 times higher in iron than it really was.
I also know from experience that when you spot analyse fruit, the nutritional content varies a lot across species, variants and also countries of origin. This last difference can be due to climate, agricultural treatment of the land or simply that an apple tree is grown in stony soil vs one with more clay from somewhere else. There is always going to be variance then and now, so any study needs to look at averaged rolling trend not a one off analysis.
Finally scanning through the data differences the ones she has chosen to look at actually means that we don't lose out much anyway when you look at it in an overall balanced diet. You never have enough calcium magnesium or sodium or potassium in a piece of fruit or a vegetable to meet your RDA in one sitting you are lucky if you get 5%, so these differences are not really going to make a major difference on its own (vitamins are a more important measure for fruits and vegetables than minerals). I would be more interested in the mineral consumption of the main drivers like grains, milk/dairy, meat/fish, seeds and nuts. The exception to that is beans and legumes which annoyingly she only looked at peas?
In summary, I think the paper is interesting but just seems to pose questions without answering them. It doesnt come across as really wanting an answer or putting her neck on the block and stating what she thinks is going on.
The key question it doesn't really answer is how to get to the bottom of methodology changes over time (lack of research on her part being the main problem) or answer what other natural variation may be at play as oppose to supply chain handling\intensive farming\yield optimisation (like growing fruits bigger than they grow naturally by irrigation and selective breeding).
Regional produce varies a lot in my experience and this is subject to drought and harvest problems as well as the retailer wanting to buy a certain grade (sorted) of product.
I'm sure that there is probably something to the mineral composition argument, although an analysis of existing literature and posing unanswered questions rather than properly looking at the variables doesn't seem to move us on very much in this paper.
The author is an academic that specialises in nutrition with her own business. I've never heard of her and had to look her up. The food industry is quite small so it is quite surprising, that her name didn't ring any bells. Nutritionalists compared to food technologists is a bit like comparing psychiatrists to any other proper medical professional...its the "wet flip floppy" end of the industry...this is probably why she skirted around the issues to do with methods and doesn't seem to grasp much of the day to day variation that happens.
She is possibly using this paper to infer credentials and it does sometimes feel like an advertorial rather than anything of substance. Her "analysis" might be there just to help her create a problem that she can then help her prospective clients to solve? I have met plenty of food consultants that are a bit like this sadly.
Ugh, don't. There's also a cheese with maggots, to be eaten when it's 'fresh' (ie when the maggots are alive) Came across that recently but can't remember where or what it was called.