Introduction

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Reports on the relation between eating frequency, lipid profile, and glucose metabolism are not new. Early evidence came from studies showing that when nibbling animals were made to acquire a gorging diet pattern, concentrations of serum lipids increased as a result of enhanced lipogenesis and synthesis of cholesterol.^1-3 The biological mechanisms that possibly underlie these alterations have been called "adaptive hyperlipogenesis."

Small, time limited trials in humans and some case-control studies also indicated that people who eat frequently tend to have lower concentrations of total cholesterol and low density lipoprotein cholesterol than people who eat a gorging diet.^4-9 Results have been less conclusive with respect to concentrations of high density lipoprotein cholesterol, apolipoproteins, and serum glucose and secretion of insulin. ^{4 6 10}

An American study involving more than 2000 participants reported that despite an increase in energy intake a higher meal frequency was related to lower concentrations of total cholesterol and low density lipoprotein cholesterol, even after adjustment for confounding variables.¹¹ Another study found an inverse relation between meal frequency and prevalence of ischaemic heart disease.¹²

Data from free living populations are limited, and it is not clear whether the effects observed in trials pertain only at the extremes of eating frequency or are continuous over the whole distribution of eating frequency. To investigate this we examined the relation between frequency of eating and concentrations of total cholesterol, low density lipoprotein cholesterol, and high density lipoprotein cholesterol in middle aged men and women in a British population based study.

	Methods

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We used data from the Norfolk cohort of the European prospective investigation into cancer. This is an ongoing prospective cohort of approximately 25 000 people aged 45-75, resident in Norfolk, and recruited from general practice registers between 1993 and 1997. All participants gave informed consent. At the baseline survey participants completed a detailed health and lifestyle questionnaire and participated in a health examination. Details of recruitment and procedures have been published.¹³

Measurements
Trained nurses carried out a health check by following standardised protocols. Anthropometric measurements were taken with participants wearing light clothes and no shoes or socks. The nurses measured height with a stadiometer to the nearest 0.1 cm after inhalation, with the participant standing as tall and straight as possible with feet together, and recorded weight to the nearest 0.1 kg. They measured circumference with a D loop, non-stretch fibreglass tape after the end of a normal expiration and at the narrowest pointthat is, the circumference between the lower rib margin and the iliac crest. If the minimum circumference was not identifiable the nurse measured the waist at the level of the navel. Hip circumference was defined as the widest point, between the iliac crest and the crotch. The nurses recorded both circumferences to the nearest 0.1 cm. Body mass index was calculated as weight in kilograms divided by height in metres squared. Waist to hip ratio was calculated as waist circumference divided by hip circumference.

Questionnaires
We assessed frequency of eating by using the question "How many times a day do you eat, including meals, snacks, biscuits with coffee breaks, etc?" We classified participants into five categories of eating frequency: one or two times a day, three times a day, four times a day, five times a day, and six or more times a day.

Statistical analysis
We used data on participants aged 45-75 who had no missing information on eating frequency, physical activity, lipid concentrations, nutrient intake, blood pressure, weight, height, or waist or hip circumference, which resulted in 14 666 participants (6890 men and 7776 women) being included in these analyses. The main reason for exclusion was missing data for physical activity, as many participants did not answer this question. We have more detailed questions on physical activity, but these had not yet been coded and analysed for the whole cohort.

	Results

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Table 1 shows the distribution of variables by category of eating frequency. Mean age did not differ linearly by eating frequency in men but was negatively related to eating frequency in women. Mean body mass index and waist to hip ratio decreased slightly and mean blood pressure increased with increasing reported eating frequency, but trends were not consistent. The percentage of current smokers and the mean alcohol intake were higher in people reporting eating two or fewer times a day. No clear trend for physical activity with eating frequency was observed in women, but men eating more frequently tended to be more likely to participate in physical or heavy manual work.

Mean concentrations of total cholesterol and low density lipoprotein cholesterol decreased with increasing eating frequency in both men and women in a continuous relation. Mean concentration was 0.29 mmol/l lower for total cholesterol and 0.26 mmol/l lower for low density lipoprotein cholesterol in men reporting eating once or twice a day compared with men eating six times or more a day; the differences for mean concentrations of total cholesterol and low density lipoprotein cholesterol in women were 0.22 mmol/l and 0.17 mmol/l. The concentration of high density lipoprotein cholesterol also decreased with increasing eating frequency in both men and women; the overall ratio of low density lipoprotein cholesterol to high density lipoprotein cholesterol decreased with increasing eating frequency.

Increased eating frequency was associated with higher daily intake of energy, as well as of fat, fatty acids, carbohydrate, and protein (table 2).

Table 3 shows mean lipid concentrations and blood pressure in men and women after adjustment for age, body mass index, waist to hip ratio, smoking status, physical activity, total energy intake, and alcohol consumption; the table also shows obesity indices after adjustment for covariates with analysis of covariance. The significant inverse relation of concentrations of total cholesterol and low density lipoprotein cholesterol to eating frequency was still present, but high density lipoprotein cholesterol concentration was no longer significantly inversely related to eating frequency in men.

Body mass index was weakly significantly associated with increasing eating frequency in men and women (after adjustment for all variables except body mass index) but in opposite directions: negatively in men and positively in women. Waist to hip ratio was still significantly negatively associated with eating frequency only in women (after adjustment for all variables except waist to hip ratio). Blood pressure was not significantly related to eating frequency in women but was positively associated in men.

We undertook multiple regression analyses of lipid concentrations on eating frequency after adjustment firstly for age, body mass index, waist to hip ratio, smoking status, physical activity, total energy intake, and alcohol consumption and secondly for these variables and for specific nutrients (fat, carbohydrate, and protein). Findings were similar, and table 4 shows regression coefficients after adjustment for covariates including specific nutrients. Concentrations of total cholesterol and low density lipoprotein cholesterol remained inversely and significantly associated with daily eating frequency. High density lipoprotein cholesterol concentration was negatively associated with eating frequency only in women. Body mass index was negatively associated in men but not in women; waist to hip ratio was negatively associated in women but not in men. Blood pressure was not independently related to eating frequency in either sex after adjustment for possible confounding factors.

We also compared the findings for ages 45-59 and 60-75 years separately. The regression slope for total cholesterol adjusted for age, sex, and covariates for each increase in eating frequency was 0.055 (SE 0.011, P<0.001) for participants aged 45-59 years and 0.041 (0.019, P=0.003) for those aged 60-75 years.

	Discussion

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In this free living British population, increased daily frequency of eating was inversely and significantly associated with lower concentrations of total cholesterol and low density lipoprotein cholesterol.

The fact that such an effect could be shown in this study is surprising, given the large potential errors in measurement. These include the single measurement of lipid concentrations to characterise individual participants as well as the assessment of eating frequency. Different participants might well interpret the question differently or report their usual eating frequency inaccurately; each person's eating pattern will also vary. Such random measurement errors are likely to obscure or minimise the effect size of any association.

Potential confounding factors
The inverse relation between blood lipid concentrations and eating frequency might be explained by confounding factorsthat is, frequency of eating might simply be a marker of particular lifestyle factors, such as physical activity or alcohol intake, that may directly influence lipid concentrations. However, the relation persisted after adjustment for possible confounding variables including age, obesity, smoking, alcohol consumption, dietary intake, and physical activity. In contrast, blood pressure was not consistently inversely related to eating frequency. We cannot exclude residual confounding, but the specificity of the independent association of eating frequency with lipid concentrations but not with blood pressure makes it unlikely that higher eating frequency was simply a marker for a healthy lifestyle. The association was also consistent in men and women and in different age groups.

Possible mechanisms
Several authors have proposed biological mechanisms that might underlie the lipid lowering effect of increased eating frequency. Fábry and Tepperman suggested that gorging animals have an adaptive metabolismthey are able to store energy from a few periodic loads of food, in contrast to nibbling animals, which feed continuously and have a steady metabolism.¹ This biological process, called "adaptive hyperlipogenesis," is characterised by higher gastrointestinal absorption of glucose and increased activity of pancreatic enzymes; increased ability to produce fat from glucose (that is, an enhanced hepatic lipogenesis possibly mediated by insulin action); increased hepatic synthesis of cholesterol; increased total mass of fat; and higher postprandial peaks of insulin and increased sensitivity to insulin in fat tissue. The increase in serum cholesterol concentration can be explained by the activation by insulin of hydroxymethyl glutaryl coenzyme A reductase, an enzyme involved in hepatic synthesis of cholesterol.⁴ Other enzymes involved in hepatic lipogenesis, such as glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, also seem to have enhanced activity in gorging animals.⁷

Implications of the findings
These metabolic adaptations to gorging may also apply in humans, leading to an increased risk of cardiovascular disease due to changes in lipid profiles and glucose metabolism. Fábry reported 30.4%, 24.2%, and 19.9% prevalence of ischaemic heart disease in men aged 60-64 years reporting eating 3, 3-4, or 5 meals or snacks daily.¹²

Conclusions
The results from this study support findings from short term experiments that concentrations of total cholesterol and low density lipoprotein cholesterol are inversely related to eating frequency in a free living general population, independently of energy intake, physical activity, or other known confounding factors. We need to consider not just what we eat but how often we eat.

	Acknowledgments

We thank the participants and general practitioners who took part in the study and the staff of EPIC-Norfolk.

Contributors: K-TK, ND, and SB originated and designed the EPIC-Norfolk population study. SO is study coordinator and organised data collection, including quality control of blood samples and measurement procedures. SB and AW carried out the nutritional analyses. RL was responsible for data management and computing overall and assisted with analyses. SMOT conducted the data analyses and wrote the paper with K-TK. K-TK is guarantor for this paper.

	Footnotes

Funding: EPIC-Norfolk is supported by research programme grant funding from the Cancer Research Campaign and Medical Research Council with additional support from the Stroke Association, British Heart Foundation, Department of Health, Europe Against Cancer Programme Commission of the European Union, Ministry of Agriculture, Fisheries and Food, and Wellcome Trust.

Competing interests: None declared.

	References

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1.	Fábry P, Tepperman J. Meal frequencya possible factor in human pathology. Am J Clin Nutr 1970; 23: 1059-1068[Abstract/Free Full Text].
2.	Cohn C, Joseph D. Changes in body composition attendant on force feeding. Am J Physiol 1959; 196: 965.
3.	Cohn C, Joseph D. Role of rate of ingestion of diet on regulation of intermediary metabolism ("meal eating" vs. "nibbling"). Metab Clin Exptl 1960; 9: 492.
4.	Jenkins DJA, Wolever TMS, Vuksan V, Brighen F, Cunnane SC, Rao AV, et al. Nibbling versus gorging: metabolic advantages of increased meal frequency. N Engl J Med 1989; 321: 929-934[Abstract].
5.	McGrath SA, Gibney MJ. The effects of altered frequency of eating on plasma lipids in free-living healthy males on normal self-selected diets. Eur J Clin Nutr 1994; 48: 402-407[Medline].
6.	Arnold LM, Ball MJ, Duncan AW, Mann J. Effect of isoenergetic intake of three or nine meals on plasma lipoproteins and glucose metabolism. Am J Clin Nutr 1993; 57: 446-451[Abstract/Free Full Text].
7.	Gwinup G, Byron RC, Roush WH, Kruger FA, Hamwi GJ. Effect of nibbling versus gorging on serum lipids in man. Am J Clin Nutr 1963; 13: 209-213[Free Full Text].
8.	Wolever TMS. Metabolic effects of continuous feeding. Metabolism 1990; 39: 947-951[CrossRef][Medline].
9.	Powell JT, Franks PJ, Poulter NR. Does nibbling or grazing protect the peripheral arteries from atherosclerosis? J Cardiovasc Risk 1999; 6: 19-22[Medline].
10.	Murphy MC, Chapman C, Lovegrove JA, Isherwood SG, Morgan LM, Wright JN, et al. Meal frequency: does it determine postprandial lipaemia? Eur J Clin Nutr 1996; 50: 491-497[Medline].
11.	Edelstein SL, Barrett-Connor EL, Wingard DL, Cohn BA. Increased meal frequency associated with decreased cholesterol concentrations; Rancho Bernardo, CA, 1984-1987. Am J Clin Nutr 1992; 55: 664-669[Abstract/Free Full Text].
12.	Fábry P, Fodor J, Hejl Z, Geizerova H, Balcarova O. Meal frequency and ischaemic heart-disease. Lancet 1968; ii: 190-191.
13.	Day N, Oakes S, Luben R, Khaw K-T, Bingham S, Welch A, et al. EPIC in Norfolk: study design and characteristics of the cohort. Br J Cancer 1999; 80(suppl 1): 95-103.
14.	Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without the use of the preparative ultracentrifuge. Clin Chem 1972; 18: 499-502[Abstract].
15.	Bingham SA, Gill C, Welch A, Cassidy A, Runswick S, Sneyd M, et al. Validation of dietary assessment methods in the UK arm of EPIC using weighed records and 24h urinary nitrogen and potassium and serum vitamin C and carotenoids as biomarkers. Int J Epidemiol 1997; 26(suppl 1): S137-S151[Abstract/Free Full Text].
16.	Clarke R, Frost C, Collins R, Appleby P, Peto R. Dietary lipids and blood cholesterol: quantitative meta-analysis of metabolic ward studies. BMJ 1997; 314: 112-117[Abstract/Free Full Text].
17.	Wald NJ, Law MR. Serum cholesterol and ischaemic heart disease. Atherosclerosis 1995; 118(suppl): S1-S5.
18.	Chen Z, Peto R, Collins R, MacMahon S, Lu J, Li W. Serum cholesterol concentration and coronary heart disease in population with low cholesterol concentrations. BMJ 1991; 303: 276-282.
19.	Colhoun H, Prescott-Clarke P, eds. Health survey for England 1994. London: HMSO, 1996. (Series HS no 4.)

(Accepted 2 September 2001)