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    Keywords: fat, fat-sugar seesaw, macronutrient intakes, NDNS, non-milk extrinsic sugar,

    sugars

    Introduction

    Dietary intake data suggest that fat and sugar have aninverse relationship. Many observational studies show

    that, in diets where a large percentage of the reportedenergy intake is provided by fat, a small percentage of

    energy in the diet comes from sugar(s) (Baghurst et al.1994; Parnell et al. 2008). McColl (1988) described this

    as the fat-sugar seesaw. Furthermore, one of thesestudies noted that consumers with a high sugar, low fat

    intake tended to have a lower body mass index thanlow sugar, high fat consumers (Bolton-Smith & Wood-

    ward 1994). This led to the suggestion that sugar energydisplaces fat energy from the diet and that, as dietary fat

    is more energy dense and potentially more likely toencourage weight gain, high sugar intakes could protect

    against obesity (Gibney et al. 1995).Dietary fat has an energy density of 37 kJ/100 g,

    which is more than twice that of sugar (16 kJ/100 g)(Holland et al. 1991). Therefore, any increase or

    decrease in the amount (weight) of sugar in the diet willhave a smaller effect on the percentage energy from

    macronutrients (and total energy) than a corresponding

    increase or decrease in the amount of fat. The concept of

    the fat-sugar seesaw has been used to suggest that thehealthy eating targets of reducing dietary sugar and fatcannot be achieved simultaneously (Drummond et al.

    1996). This led to the conclusion that dietary advicewould be more effective if focused on fat reduction,

    while setting no limits on the consumption of carbohy-drates, including sugar (Drummond et al. 1996; Gibson

    1997). Because sugar is combined with fats in the manu-facture of many processed foods, an alternative argu-

    ment is that high sugar foods can act as a vehicle fordietary fat (Emmett & Heaton 1995; Macdiarmid et al.

    1998). Furthermore, Macdiarmid et al. (1995) cast

    doubt on the fat-sugar seesaw concept, observing that itdepends on whether macronutrients are calculated andanalysed as percentages of energy intake or weight in

    grams.Central to the evidence for a fat-sugar seesaw is the

    inverse relationship between intakes of fat and sugar inpeoples diets. Daily dietary intakes show variation,

    both between individuals and on an individual basis(e.g. de Castro 1991). These variations tend to produce

    a wide range of different correlations between various

    macronutrient intakes in individuals, perhaps suggestingthat people respond differently (i.e. that they exhibit

    individual differences) to alterations in the macronutri-ent composition of the diet. Having said that, however,

    each correlation is poorly estimated from just sevendaily observations (such as when taken from 7-day food

    intake records); therefore, it is possible that much of thevariation in correlation is due to sampling rather than

    differences in the dietary behaviours of people. More-over, sampling distribution of the correlation coefficient

    is complex, usually being described through approxima-tions, such as Fisher (1922) and Konishi (1978).

    To test the concept of the fat-sugar seesaw, this studyexamined correlations between dietary macronutrients,

    between individuals and on an individual basis over a7-day period using dietary data from the National Diet

    and Nutrition Survey (NDNS) for adults, which werecollected in 2000 and 2001 (Henderson et al. 2003).

    We also examined relationships between the macronu-trient compositions of foods in the Food Standard

    Agencys (FSAs) Nutrient Databank. The NutrientDatabank includes energy and nutrient information on

    some 7000 foods, and was used by the NDNSresearchers to calculate energy and nutrient intakes

    from the weights of foods and drinks recorded by theparticipants.

    Methods

    Collection of the NDNS data used here took placebetween July 2000 and June 2001 and included a nation-

    ally representative sample of adults aged 1964 yearsfrom England, Wales and Scotland (Henderson et al.

    2003). Food intake records, using the 7-day weighedfood intake method, were provided by n = 1724 people.

    In the current analysis, total energy intake was divided

    into seven components: fat, total sugar, intrinsic sugars,non-milk extrinsic sugars (NMES), non-sugar carbohy-drates, protein and alcohol. Here total sugar refers to all

    intracellular and extracellular dietary sugars and milksugars, whether these were added to foods or are natu-

    rally occurring. Intrinsic sugar is that contained withinthe cell walls of foods (such as in fruits) and milk sugars

    (e.g. lactose). Non-milk extrinsic sugars are those notcontained within the cell walls, such as sugar from honey

    and table sugar, but excluding milk sugars. Non-sugar

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    the various sugars were (r = -0.40, n = 1724, P < 0.001)for total sugar; (r = -0.22, n = 1724, P < 0.001) for

    NMES; and (r = -0.33, n = 1724, P < 0.001) for intrin-sic sugars.

    Within-subject associations

    Table 2 shows the mean within-subject correlationsbetween the weights (g/day) of the various macronutri-

    ents of the reported diet as calculated from each sub-jects seven separate daily intake records. All correlation

    values in Table 2 are positive and statistically significant(P < 0.001), indicating not only a lack of fat-sugar

    seesaw in the diets of individuals, but the opposite. Thepositive correlations between the macronutrients

    (Table 2) show that (on average) on days when subjects

    consumed more of one macronutrient than they did onother days, they also consumed more of all of the othermacronutrients. For example, on days when subjects

    consumed more fat than they did on average on otherdays, they also consumed more intrinsic sugar, more

    NMES and more total sugar, rather than less, as wouldbe predicted by the fat-sugar argument.

    Figure 2 shows a histogram of the distribution ofwithin-subject correlations between the weights (g/day)

    of fat and total sugar, calculated from each individuals

    seven separate daily intake records. The mean cor-relation between the weights (g/day) of fat and total

    sugar obtained was positive (r = 0.24, n = 12 068,

    P = < 0.001). This differed significantly from zero, thus

    indicating that there were more positive than negativecorrelations between fat and total sugar (g/day).

    Figure 2 also shows the theoretical distribution ofcorrelations between two variables estimated from

    10 000 simulated samples of size 7 (corresponding tothe seven daily food intake records), when the true

    correlation between the two variables is r = 0.24. The fitbetween the theoretical distribution of correlations (line

    in Fig. 2) and the observed distribution of correlations(bars in Fig. 2) from the subjects data is remarkably

    close.

    Associations within the Nutrient Databank

    Figure 3 illustrates a scatter plot of the amount (g/100 g)

    of fat and total sugar in each of the n = 6990 food itemsin the Nutrient Databank that were included in the

    analysis. The correlation between fat and total sugar inthe food items of the Nutrient Databank is very weakly

    positive (r = 0.03, n = 6990, P = 0.006) and many of thefood items are concentrated in the bottom left of the

    plot. This association is also illustrated in log scaleformat for visual emphasis (Fig. 3b). Two clusters can

    be seen within this plot, one smaller cluster of foods

    containing substantially more of both fat and sugar than

    those in the other larger cluster. Closer inspection of theNutrient Databank revealed that items in this smallercluster were mostly the more processed and composite

    foodstuffs, whereas the larger cluster consisted more ofraw food ingredients. However, even within the smaller

    cluster, which contained foods with a sugar content of atleast 10 g/100 g, there was a weak, but positive, corre-

    lation (r = 0.09, n = 1539, P < 0.001) between fat andsugar, whereas this association was negative in the larger

    cluster (r = -0.18, n = 5451, P < 0.001).Table 3 shows the level of associations among fat,

    sugars, carbohydrate and protein in the n = 6990 foods

    in the Nutrient Databank. Fat showed a significant posi-tive correlation with total sugar, NMES, carbohydrateand non-sugar carbohydrate, and a significant negative

    correlation with intrinsic sugar. Protein showed a sig-nificant negative correlation with total sugar, intrinsic

    sugar, NMES, carbohydrate and non-sugar carbohy-drate. Thus, fat had a positive correlation with all

    macronutrients (except intrinsic sugar) whereas proteinhad a positive correlation with fat and a negative cor-

    relation with all other macronutrients.

    Table 1 Mean daily energy and macronutrient intakes

    n

    Women Men All

    958 766 1724

    Mean ( SD) Mean ( SD) Mean ( SD)

    Energy (MJ) 8.03 (2.52) 8.22 (2.65) 8.11 (2.58)

    Energy (kcal) 1921(603) 1967(634) 1940 (617)

    Ener gy intake: BMR 1.37 (0.46) 1 .07 (0.36) 1 .24 (0.44)

    CHO (g) 232.2 (78.5) 236.5 (81.4) 234.1 (79.8)

    Fat (g) 71.1 (27.0) 73.6 (29.1) 72.2 (28.0)

    Protein (g) 72.9 (23.3) 76.0 (31.1) 74.3 (27.1)

    Alcohol (g) 15.6 (21.4) 14.6 (19.8) 15.2 (20.7)

    Total sugar (g) 100.7 (46.9) 102.0 (47 .8) 101.3 (47 .3)

    Intr insic sugar (g) 38.4 (20.2) 38.3 (20.2) 38.3 (20.2)

    NMES (g) 62.3 (39.8) 63.7 (40.9) 62.9 (40.3)

    CHO (% energy) 46.5 (7.1) 46.3 (7.4) 46.4 (7.2)

    Fat (% energy) 32.6 (6.0) 32.8 (6.4) 32.7 (6.2)

    Protein (% ener gy) 15.7 (3.1) 16.0 (3.7) 15.8 (3.4)

    Alcohol (% energy) 5.3 (6.7) 4.9 (6.3) 5.1 (6.5)Total sugar (% ener gy) 20 .0 (6.6) 19.8 (6.7) 19.9 (6.6)

    Intr insic sugar (% ener gy) 7 .9 (3.9) 7.7 (3.9) 7.8 (3.9)

    NMES (% energy) 12.1 (6.2) 12.1 (6.4) 12.1 (6.3)

    BMR, basal metabolic rate; CHO, carbohydrate; NMES, non-milk extrinsic

    sugar; SD, standard deviation; % energy, percentage energy (see Methods).

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    Discussion

    Principal findings

    In this study of the correlations between fat and sugar(s)in the diets of NDNS subjects, and the FSAs Nutrient

    Databank, which was used to calculate energy and

    nutrient intakes from the weights of foods and drinksrecorded by the subjects, the correlations between fat

    and sugar(s) were calculated in five ways: (1) betweenindividuals in percentage terms (percentage energy); (2)

    between individuals in absolute amounts (g); (3)between individuals in amount (g) relative to BMR; (4)

    within individuals over 7 days; and (5) between food

    Fat

    0 100 200 300 400 50 100 150 200

    50

    100

    150

    200

    0

    100

    200

    300

    400

    Sugar

    Non-sugar CHO

    0

    100

    200

    300

    50 100 150 200

    50

    100

    150

    20

    0

    0 100 200 300

    Protein

    Figure 1 Scatter plot matrix of individual means (g/day) of the macronutrient components.To reduce clutter, axes are marked at the top and bottom, and

    left and right, on alternate plots. CHO, carbohydrate.

    Fat and sugar relationship in the NDNS 217

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    items in the Nutrient Databank. Only when examining

    the correlation between fat and sugar(s) between indi-

    viduals in percentage terms (percentage energy) was thefat-sugar seesaw evident; in all other methods, the cor-relation between fat and sugar(s) was positive.

    Results showed that in a free-living human popula-tion, macronutrient intakes do not exhibit a fat-sugar

    seesaw effect when expressed in absolute terms (i.e.weight in g). There was no inverse relationship between

    any one macronutrient and another, and specificallythere was no inverse relationship between fat and intrin-

    sic sugar, NMES or total sugar, but rather there was a

    Table 2 Within-subject correlations for the macronutrient components of the diet (g/day)

    Fat Total sugar Intrinsic sugar NMES CHO Non-sugar CHO Protein

    Fat r = 1.00

    Total sugar r = 0.24 r = 1.00

    Intrinsic sugar r = 0.15 r = 0.51 r = 1.00

    Non-milk extrinsic sugars r = 0.23 r = 0.85 r = 0.11 r = 1.00

    Carbohydrate r = 0.42 r = 0.68 r = 0.42 r = 0.58 r = 1.00

    Non-sugar carbohy dr ate r = 0.41 r = 0.20 r = 0.20 r = 0.16 r = 0.79 r = 1.00

    Protein r = 0.50 r = 0.19 r = 0.24 r = 0.13 r = 0.36 r = 0.36 r = 1.00

    For all correlations, n = 12 068, P < 0.001.

    NMES, non-milk extrinsic sugar; CHO, carbohydrate.

    Fat-sugar correlations

    Correlation

    Frequency

    1.0 0.5 0.0 0.5 1.0

    0.0

    0.2

    0.4

    0.6

    0.8

    Figure 2 Histogram of within-individual correlations for fat and

    total-sugar intake (g/day), calculated for each subject. The theoretical

    sampling variation for a population with a constant correlation is also

    shown as the superimposed smooth curve.

    0.01

    0.1

    1

    10

    100

    0.01 0.1 1 10 100

    Fat (g/100g)

    Totalsugar(g/100g)

    (a)

    (b)

    0

    10

    20

    30

    40

    50

    60

    70

    80

    90

    100

    0 20 40 60 80 100

    Totalsugar(g/100g)

    Fat (g/100g)

    Figure 3 (a) Fat and sugar amount per 100 g in all items in the National

    Diet and Nutrition Survey food composition database. (b) The same plot

    on a log scale.

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    mild positive one. In most cases, this lack of inverserelationship was not a consequence of dietary behav-

    iour; rather it is possibly connected to the macronutrientcomposition of specific food items that the study par-

    ticipants chose to consume. Given that mean within-subject correlation between absolute intakes (i.e. weight

    in g) of fat and total sugar was positively associated, itcan be concluded that fat and sugar do not displace each

    other in absolute terms (i.e. gram for gram); at least this

    was the case in free-living individuals self-reporting their

    habitual diets. Our results indicate that on days whenmore of one macronutrient (e.g. fat) is consumed com-pared with other days, then there is also a tendency to

    consume more of the other macronutrient [in this casesugar(s)] as well.

    Comparison with other studies

    Numerous epidemiological studies have shown an

    inverse relationship between sugar and fat consumptionwhen macronutrients are expressed as their percentage

    contribution to total energy intake (e.g. Baghurst et al.

    1994; Bolton-Smith & Woodward 1994; Gibney et al.1995; Alexy et al. 2003; Dwyer et al. 2003); indeed,such relationships were observed in the current analysis.

    Furthermore, when Australian adults were divided intoquintiles (fifths) of percentage energy intake from fat,

    Baghurst et al. (1994) found significant negative trendsof percentage energy intake from fats and sugars.

    Baghurst et al. (1994) grouped sugars differently than inthe current analysis, but they reported significant nega-

    tive trends of percentage energy intake from fats and

    simple sugars (monosaccharides and disaccharideswhether occurring naturally or added to foods and

    equivalent to the sum of intrinsic sugars and NMESreported in the current paper), natural sugars (all sugars

    other than those added to processed foods) in both menand women, and for added sugars (all sugars that had

    been added to processed foods or added by the con-sumer) in men, but not women. Calculating absolute

    intakes as weight in g of sugars from the publishedvalues of Baghurst et al. (1994) shows that the weight of

    simple sugars, natural sugars and added sugars for men,but not women, also decreases with quintiles of increas-ing percentage energy from fat. Thus, the data presented

    by Baghurst et al. (1994) appear to show a fat-sugarseesaw even when sugar is expressed as weight and fat

    as a percentage of energy intake, at least in men.When the NDNS data used in the current analysis

    were divided up into quintiles of percentage energy fromfat using the same methods as Baghurst et al. (1994),

    similar relationships to those reported by Baghurst et al.(1994) were apparent; weight of intrinsic sugars (g),

    total sugars (g) and percentage energy from NMES

    decreased with increasing quintiles of percentage energyintake from fat (values not shown here), suggestive of afat-sugar seesaw. This is an apparent contradiction to

    the results of the regression analysis, conducted on thesame data, showing positive correlations between fat

    and sugar(s) (Table 2), and contesting the fat-sugarseesaw; the weight of fat and sugar(s) in the diet appears

    to have contradictory relationships, being negativewhen intakes of sugar(s) are considered against quintiles

    of the percentage energy intake from fat, yet positive

    Table 3 Food database correlations in the macronutrient composition of foods (expressed as g/100 g of food)

    Fat Total sugar Intrinsic sugar Extrinsic sugar CHO Non-sugar CHO Protein

    Fat r = 1.00

    P < 0.001

    Total sugar r = 0.03 r = 1.00

    P = 0.006 P < 0.001

    Intrinsic sugar r = -0.02 r = 0.38 r = 1.00

    P = 0.041 P < 0.001 P < 0.001

    NMES r = 0.04 r = 0.96 r = 0.11 r = 1.00

    P < 0.001 P < 0.001 P < 0.001 P < 0.001

    CHO r = 0.09 r = 0.72 r = 0.27 r = 0.70 r = 1.00

    P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001

    Non-sugar CHO r = 0.10 r = 0.07 r = 0.02 r = 0.07 r = 0.74 r = 1.00

    P < 0.001 P < 0.001 P = 0.086 P < 0.001 P < 0.001 P < 0.001

    Protein r = 0.17 r = -0.24 r = -0.12 r = -0.22 r = -0.20 r = -0.06 r = 1.00

    P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001

    For all correlations, n = 6990.

    CHO, carbohydrate; NMES, non-milk extrinsic sugar.

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    when considered against intakes of fat expressed asweights (g). This apparent paradox is a result of the

    seesaw in percentage energy from fat and absoluteamount of sugar (g) being an artefact rather than a real

    dietary effect; this is simply a weaker version of thecorrelation, expressed as percentage energy from fat and

    percentage energy from sugar that arises from the mereoperation of taking percentages instead of using weight

    in the analysis. Furthermore, if sugar, fat, protein andnon-sugar carbohydrate are independent variables (i.e.no seesaw effect), then sugar (g) and the percentageenergy from fat will be negatively correlated. These will

    even be negatively correlated when there is a weak posi-tive correlation between sugar (g) and fat (g). The

    reason for this is that expressing one (or more) of themacronutrients as a percentage, whether percentage

    contribution to energy or total weight, introduces adependency between the macronutrients. Consider, for

    example, a range of theoretical foods that comprise onlyfat and sugar in variable amounts. When the macronu-

    trient composition of these foods is expressed as a per-centage of total energy content of the food, there must

    be a perfect negative correlation (or seesaw) betweenpercentage energy from fat and percentage energy from

    sugar, because the total must equal to 100% and foodsthat have a high percentage energy from fat must have a

    low percentage energy from sugar, and vice versa. If

    further macronutrients (non-sugar carbohydrate andprotein) are introduced into the model, the same effect

    remains in operation, albeit less strongly. The mecha-

    nism for this is that foods that have a high percentageenergy from fat must have a low percentage energy fromthe sum of the remaining macronutrients (in this case

    sugar, non-sugar carbohydrate and protein).At 37 kJ/100 g, the energy density of dietary fat is

    approximately 2.3 times that of sugar (16 kJ/100 g)(Holland et al. 1991). This has the effect of strength-

    ening the correlation between fat and sugar when one,or indeed both, are expressed as their percentage con-

    tribution to total energy; the association would still benegative if fat and sugar had the same energy densities

    because the different energy densities of fat and sugar

    are constants and have a simple scaling effect. Theabove negative relationships between percentageenergy from fat and weight (g) of sugar(s) are evident

    even in dietary data fabricated from random numbersemphasizing that the fat-sugar seesaw is a mathemati-

    cal artefact rather than a dietary effect. This can beseen by using the random number function of a

    spreadsheet program to generate fat, sugar, non-sugarcarbohydrate and protein values for theoretical foods

    and plotting percentage energy from fat against weight

    (g) of sugar. The authors may be contacted for such aspreadsheet.

    That fat and sugar, or even fat and carbohydrate, arereciprocally related in percentage terms in the diet is

    almost inevitable because they are the main energy-providing macronutrients in typical Western style diets.

    The contribution of the other main macronutrient(protein) to daily energy intakes tends to show less

    variation. When expressed as absolute amounts(g/100 g), there is a positive relationship between fat

    and sugar in peoples diets (Emmett & Heaton 1995;Macdiarmid et al. 1995; Drewnowski et al. 1997), and

    as reported here and elsewhere (Stubbs et al. 2001) therelationship between fat and sugar in ready-to-eat foods

    in food composition tables is far less evident (see below).In the present study, clear positive relationships were

    evident among the macronutrients (g) in the recordeddietary intake data. When macronutrient intakes were

    expressed as weight (g), and energy requirements weretaken into account, albeit approximately by calculating

    intake relative to estimated BMR, the correlationsbetween pairs of macronutrients were all positive. Thus,

    as expected, people with higher energy requirementstended to achieve the necessary higher energy intakes by

    consuming more of all the macronutrients and not bydiscernibly selecting more of one and less of another as

    a seesaw effect would suggest.

    The estimated correlations between fat and totalsugar varied greatly between subjects (Fig. 2). For

    example, for some people (i.e. those with positive cor-

    relations between fat and total sugar), on the days onwhich they consumed more fat they also consumedmore total sugar, whereas for others (i.e. those with

    negative correlations between fat and total sugar) when-ever they consumed more fat they consumed less total

    sugar. Thus, at face value, Figure 2 could be taken tosuggest that there are different dietary behaviour phe-

    notypes, one in which the fat-sugar seesaw operated intheir diet selection and the other in which it does not.

    However, this could all be explained by sampling varia-tion. The fit between the theoretical range of correla-

    tions (line in Fig. 2) and the observed range of

    correlations (bars in Fig. 2) in the subjects is remarkablyclose. Thus, it is not possible to infer variation at all inwithin-subject macronutrient correlation.

    Associations within the Nutrient Databank

    In the analysis when the contributions of fat and sugar

    were plotted against each other (Fig. 3b), thereappeared to be two main clusters of foods stemming

    from within the Nutrient Databank. Closer inspection

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    revealed that the relationship between fat and sugartended to differ between the two cluster groups, such

    that, foods that made up the smaller cluster were typi-cally the more processed foods, which tend to have

    relatively large amounts of both sugar and fat. Com-mercially available snack foods tend to be mixtures of

    fats and sugars (e.g. chocolate), or fats and starches(e.g. biscuits). They tend to be low in protein and have

    a low moisture content (Whybrow et al. 2007). Com-monly within the food supply chain, sugar acts as a

    vehicle for fat by increasing the palatability of high-fat foods (Emmett & Heaton 1995), whereas less-

    processed foods (such as fruits) and raw foodingredients (such as margarine, cooking oils, flour and

    table sugar) tend to be composed predominantly of fat,starch or sugar. Another group of foods that can be

    high in fat with little or no sugar, but with a relativelylarge amount of protein, is meat (and some fish). In

    processed foods, sugar(s) tend to be positively associ-ated with fat, while in raw foods/ingredients they tend

    not to be. The correlations between fat and sugar in thetwo clusters are consistent with this; being positive in

    the smaller cluster and negative in the larger cluster.Overall, these clusters may be reflected in the associa-

    tions in the overall diet, depending on how much thediet is comprised of processed foods or less-

    processed foods. Accordingly, there may be a different

    relationship between fat and sugar in the context of theoverall diet dependent upon whether or not the sugar

    comes from processed or raw foods. However, the

    overall relationship between fat and sugar(s) in thediets of individuals in the NDNS was positive.

    In this study, a seesaw effect was not evident from the

    assessment of the dietary behaviour of free-living sub-jects not undergoing any specific dietary interventions.

    Having said that, a seesaw effect may arise in subjectsattempting to modify their weight by altering their diet.

    This is because, while weight loss diets have many strat-egies, reducing fat or carbohydrate intake is often sug-

    gested. Under these circumstances, individuals mightcompensate by increasing their intake of other macro-

    nutrients, in absolute terms, relative to what they were

    consuming beforehand. However, this does not appearto be the case for ad libitum low-fat (Carmichael et al.1998) or low-carbohydrate diets (Samaha et al. 2003),

    although more rigorous manipulations, such as Atkinstype diets, which severely reduce the amount of carbo-

    hydrate consumed in the diet, do result in an increase inthe intake of other macronutrients (Gardner et al.

    2007). The overall conclusion seems to be that compen-sation is weak, while supplementing the diet with either

    fat or sugar does not produce macronutrient-specific

    compensation (Raben et al. 2002; Mazlan et al. 2006;Whybrow et al. 2007).

    The relationship between fat and sugar may also bedifferent in populations whose diets comprise very few

    processed foods. It has been suggested that a decreasein the consumption of extrinsic sugars could also bring

    about a decrease in fat consumption because of thepositive association between these two nutrients in

    many processed foods (Emmett & Heaton 1995). Thelack of association between fat and sugar in less-

    processed foods suggests that in diets with few pro-cessed foods, a decrease in sugar intake may lead to an

    increase in fat intake. In part, this would dependon how raw foods and ingredients are combined in

    the diet.Comparing dietary composition in percentage terms

    alone can be misleading. It is a feature of compositionaldata to introduce negative correlations between macro-

    nutrients, because when any set of independent vari-ables is expressed as a percentage of the total, these

    percentages are more likely than not to be negativelycorrelated. In such circumstances, the correlation is a

    statistical artefact, which gives little real informationabout how the original variables relate to one another,

    and only when dietary intakes are examined as absolutevalues (g), as well as percentages, can the interrelation-

    ships between the different macronutrients be studied

    fully.

    Strengths and limitations of the studyOne issue that casts a shadow over all dietary analysissurveys (such as the NDNS used here) is the misreport-

    ing of food intake. For example, it is well known thatpeople tend to report lower intakes than they have con-

    sumed, to eat less than they habitually do and even tochange their pattern of consumption (Macdiarmid &

    Blundell 1998; Stubbs et al. 2003). With regard tounder-reporting, Emmett and Heaton (1995) found that

    while sugar and fat intakes were positively related whenpeople reporting low energy intakes were included in the

    analysis, the relationship became non-significant when

    low energy reporting was accounted for. The authorsattributed this to biased misreporting of certain foods.Moreover, misreporting is often clearly evident when

    dietary intakes are implausibly low for someone inassumed energy balance (Black 2000). Unfortunately,

    however, there is no satisfactory way to remove misre-porting effects from a dietary survey. Omitting subjects

    with lower reported intakes only causes bias and higherreported intakes are also affected by misreporting,

    because they are more likely in those with higher activity

    Fat and sugar relationship in the NDNS 221

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    levels. For these reasons, we did not attempt any adjust-ment or editing of the data to deal with misreporting. To

    check whether misreporting might have influenced ourresults, we looked for associations with misreporting

    indicators (i.e. reported energy intake relative to esti-mated energy requirements) and found none; there was

    no significant association between within-subject fat-sugar correlation and energy intake relative to estimated

    energy requirements.The NDNS data used here was collected over a

    decade ago. Accordingly, the macronutrient composi-tion of some processed foods will have changed over

    that time, particularly the fat and sugar content offoods. Such changes can influence the strength of asso-

    ciations between fat and sugar in the foods peoplechoose to consume and can also influence overall diet.

    These are, however, unlikely to alter the direction of theassociations.

    Conclusions

    In the diets of free-living populations, macronutrientintakes do not show a seesaw relationship when

    expressed in absolute terms (i.e. g/100 g). There is noindication that people strictly choose between fats and

    sugar, or that higher intakes of one macronutrient areassociated with lower intakes of the other, as might be

    interpreted from the fat-sugar seesaw argument.Comparing diet composition in percentage terms

    alone can be misleading. It is only when dietary intakesare examined as absolute values, as well as relative to

    their contribution to energy, that the interrelationshipsbetween the different macronutrients can be studied

    fully.

    Acknowledgements

    This work was supported by The Scottish Governments

    Rural and Environment Science and Analytical ServicesDivision (RESAS).

    Conflict of interest

    The authors have no conflict of interest.

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