Table of Contents
Introduction
In the last 4 lessons we discussed the 3 macronutrients (protein, carbohydrate, and fat), and we discussed fiber, all of which are the building blocks of foods we eat. In this lesson we will discuss alcohol, the last macronutrient, and its impact on the dieting process as well as overall health.
Note: The impact of alcohol on health is controversial, and I discuss this in a lot of detail below to try to present a fair overview of the literature. For those who do not wish to read through all of this, you can get all the main points of this lesson by:
- reading the summary paragraph in the section of the short-term impact of alcohol on dieting and exercise
- the 2020-2025 Dietary Guidelines for the Americas recommendation regarding alcohol intake listed at the beginning of the section of the long-term impact of alcohol on health
- the conclusion at the end
Short-term impact of alcohol on dieting and exercise
Considerations for short-term intake are much different than long-term intake. Short-term refers to within a single session. Repetitive binge-drinking has negative impacts on health overall (as mentioned below); intermittent episodes of non-binge drinking are considered here.
Impact on caloric consumption
A
Note: Alcohol has 7 kcal per gram, but many alcoholic drinks also have added sugar further increasing the caloric content. All of this counts if one is counting calories. Alcohol does have a relatively high thermic effect of feeding (more similar to that of protein than to carbohydrate or fat), but as most people consume relatively low amounts of alcohol this will not have a meaningful impact on dieting overall.
A fairly recent study attempted to examine the impact of decreasing alcohol intake in an overall weight management behavioral intervention.(Kase, 2016) Among other things, generic advice was given to decrease alcohol consumption. Over a 1 year time span a decrease in alcohol consumption was not associated with weight changes overall. However, when looking at subjects who were determined to have a high level of behavioral impulsivity, alcohol reduction was associated with weight loss. It is possible that these individuals benefit most from alcohol reduction due to decreased disinhibition (leading to less caloric consumption). It is also possible that decreased alcohol intake led to a decrease in the general expectancy that one will eat more calories when consuming alcohol, thus leading to fewer calories being consumed on occasions of alcohol intake.
Impact on exercise
A
Summary
Thus, overall there is no strong evidence in the literature that a low level of alcohol intake (consistent with the guideline listed below) will have a harmful effect on dieting and resistance training progress. However, for individuals who are more prone to eating larger amounts with alcohol intake, or who are more prone to take the mentality after consuming alcohol that they have “ruined” their dieting for the day and thus should do whatever they want and get back on track tomorrow, minimizing alcohol consumption would likely be helpful when actively dieting to lose weight.
Long-term impact of alcohol on health
The following note shows one set of guidelines for alcohol intake.
Note: Regarding alcohol intake, the 2020-2025 Dietary Guidelines for Americans recommends:
- 1 alcoholic drink-equivalent should be defined as containing 14 grams of pure alcohol
- 12 fluid ounces of regular beer (5% alcohol), 5 fluid ounces of wine (12% alcohol), 1.5 fluid ounces of 80 proof distilled spirits (40% alcohol)
- Females should consume no more than 1 drink daily and should especially avoid binge drinking (no more than 3 drinks in one setting)
- Males should consume no more than 2 drinks daily and should especially avoid binge drinking (no more than 4 drinks in one setting)
- People who do not currently drink alcohol should not begin drinking alcohol. Additionally, people should not drink alcohol if they are pregnant (or may be pregnant), younger than 21 years old, recovering from alcoholism or unable to control the amount they drink, have certain medical conditions, or take certain medications. Adults over 60 years old should not drink if they plan to drive or operate machinery or participate in activities that require skill, coordination, and alertness
The majority of the literature agrees with not going above these guidelines. However, there is significant controversy regarding whether alcohol intake within these guidelines provides net health benefit or harm relative to abstaining from alcohol completely. There was even controversy when writing the 2020-2025 Dietary Guidelines for Americans regarding this specific point (see discussion here). I will attempt now to present a fair overview of this debate.
Review articles
In 2016 a consensus document specifically focused on beer came to many of these same findings as the prior reviews.(de Gaetano, 2016) These authors also state that unless there is concern for a high risk of alcohol-related cancer there is no reason to discourage healthy adults with regular light-to-moderate volume beer intake to decrease their consumption, but they additionally add that there is no evidence that adult abstainers who start drinking alcoholic beverages in moderation reduce their risk of chronic disease.
Note:
A 2018 review article discusses several prior studies and reviews indicating a benefit of low level of alcohol intake on cardiovascular mortality and other health parameters.(O’Keefe, 2018) They do note that benefits are seen more frequently in middle aged and older individuals than younger aged, there are ethnic differences, and many benefits last <24 hours (which may help justify regular low level intake for sustained benefit rather than intermittent intake). They also state that studies show it is difficult to predict who will be at risk for problem drinking once they begin and they cite the American Heart Association’s recommendation that nondrinkers should not be advised to start drinking.
A separate 2018 review comes to similar conclusions.(Goel, 2018) Authors here also note that benefits are more often seen as one’s age increases and the risks of developing drinking problems and binge drinking may outweigh the benefits for the younger population. They also note ethnic differences. They conclude that 1-2 drinks daily is not dangerous but abstainers should not be encouraged to start drinking as there is no way to predict if a person would only consume alcohol in moderation after starting.
Note: This is one of several topics in the field of nutrition where industry seems to exert some level of influence on research findings. While research sponsored by industry is not necessarily biased or untrustworthy, it is generally worth considering if the majority of the industry-sponsored research leans one way while non-industry-sponsored research takes a different point of view. See below for a more concrete example of the alcohol industry influencing research.
Finally, now entering 2020 we have another large review article on the impact of moderate alcohol consumption on cardiovascular disease, echoing several of the findings discussed in above reviews.(Chiva-Blanch, 2019) They note that women absorb alcohol differently due to lower body water, smaller stature, and lower gastric alcohol dehydrogenase and that many studies have found sex-specific differences. Benefits for all-cause mortality are typically only seen in white & Hispanic populations, not black/Indian/Chinese, and Asians seem to have a higher risk of hypertension & stroke at the same level of intake. Harmful effects of abusive or heavy intake however are the same throughout the globe.
Moderate alcohol consumption seems to attenuate inflammation, decrease fibrinogen & fibrin D-dimer, increase tissue plasminogen activator & plasminogen concentrations, inhibit platelet reactivity, and increase HDL cholesterol. Risk of hypertension increases linearly with alcohol intake though <1-2 drinks daily with meals may not be detrimental. Low-to-moderate alcohol intake is associated with decreased risk of heart failure and in people with cardiovascular disease a lower incidence of all-cause mortality. However, they mention some data indicates benefits for all-cause mortality are only seen in generally older populations. They note consumers who consider alcohol intake as healthy for cardiovascular disease have been shown to consume 1.5x more alcohol than those who do not consider it healthy. They conclude stating it would be wise to suggest low-to-moderate alcohol consumption among current drinkers and to never recommend drinking in order to improve health.
In addition to all of the overview articles above, I
Mendelian randomization analysis
In 2014 an important Mendelian randomization analysis was conducted.(Holmes, 2014) For a review of Mendelian randomization studies, particularly as it pertains to this analysis, please read through the following note prior to continuing. This can be a somewhat complicated concept and it is certainly not necessary to read through this note to understand the main point of this analysis discussed below.
Note: Mendelian randomization studies essentially function as long-term randomized controlled trials. The idea is that a genetic variant is linked to a variable (ie, alcohol intake) which is then linked to an outcome (ie, coronary heart disease). For this analysis they look at genetic mutations of ADH1B, which are known to be associated with decreased alcohol consumption. Thus, people with this mutation are “randomized” into a group that consumes less alcohol. Ideally this would be the only difference and thus if this group had different health outcomes it would be due to drinking less alcohol.
However, in practice there are other considerations, and this has led to some criticism of Mendelian randomization studies regarding alcohol intake. Some of these include:
- As this mutation alters the metabolism of acetaldehyde (a byproduct of alcohol breakdown in the body), if acetaldehyde directly influences any health benefits/harms then it will be unclear if health changes are due to different amounts of alcohol intake vs. different profiles of acetaldehyde metabolism.
- If this mutation associates with any other factors there can be confounding. As one example, this could occur if people who drink less alcohol are less likely to live a “party lifestyle” and are more likely to associate with other similar-minded individuals. Thus, there would be social differences between genetic carriers and non-carriers of the mutation and this could impact health outcomes.
- If this mutation causes less alcohol consumption and moderate alcohol consumption is actually beneficial then this mutation may be associated with harm. However, if this mutation causes less binge drinking and binge drinking is detrimental then this mutation may be associated with benefit. Given potential competing factors, it can be hard to draw any definitive conclusion about what influences the actual health outcomes.
If curious,
This analysis was based on individual participant data from >260,000 people across 56 studies. They found that carriers of the variant allele consumed 17.2% less units of alcohol weekly, had an odds ratio of 0.70 of being in the top 1/3 of drinkers, had an odds ratio of 0.78 for binge drinking, and had an odds ratio of 1.27 of being abstainers from consuming alcohol. Thus, carriage of the variant allele was associated with all types of self-reported drinking behavior, which is important as this could then be used for analysis in individuals drinking amounts along the spectrum of low, moderate, and high alcohol quantities. The idea is that in any predefined bin of alcohol intake, carriers would be drinking a lower amount of alcohol in that bin relative to non-carriers.
Their main finding is that for people who consumed alcohol, carriers had decreased odds (0.86) of coronary heart disease (“CHD”) compared to non-carriers. The same protective effect was seen at intakes of 0-6 units weekly, 7-20 units weekly, 21+ units weekly. Thus, as carriers consumed less alcohol in all of these different groups of alcohol intake, the fact that they had lower risk of CHD implies that alcohol increased the risk of developing CHD. Importantly, the risk was not decreased in abstainers, which implies the genetic variant itself did not provide protection from CHD.
Concerns of abstainer bias
In
Note: Most prospective studies on alcohol intake and its impact on mortality have historically considered people who abstain from alcohol intake to be a control group. They have then compared low, moderate, and heavy alcohol intake to the abstainers (different studies have defined low, moderate, and heavy in different ways).
The potential issue here is that many people who are former drinkers have quit in part due to health problems related to their prior drinking. When they enroll in one of these studies they may still be placed in the control group as they are currently abstaining from alcohol intake. This will lead to the abstainer group having worse outcomes and thus people drinking a low level of alcohol intake may appear to have better health outcomes in comparison. To try to eliminate this “abstainer bias”, it is important to separate “lifelong abstainers” from “former drinkers”. One caveat is that lifelong abstainers may have other confounding factors (ie, be part of certain religions or communities that abstain from alcohol that could then influence health outcomes in other ways).
Here they specifically looked at 87 prospective studies that considered the relationship between alcohol intake and all-cause mortality. They note that historically studies showed a low level of drinking yielded better outcomes then not drinking at all. When looking at all 87 studies they found a protective effect of occasional and low volume alcohol drinking for all-cause mortality (relative risk of 0.84 and 0.86, respectively). However,
Note: A commentary on this study brought up concerns that most of the studies only assessed alcohol intake once while drinking patterns change over time and that in a US national survey >50% of people describe themselves as lifetime abstainers in follow-up after reporting drinking previously.(Rehm, 2016) The vast majority of large epidemiologic studies in the nutrition field only measure exposure level one time at baseline, and this is a common (and valid) criticism as many people will have exposure levels vary over time. This is discussed further below. The concern of people misremembering or simply lying about prior exposure is also a common occurrence in the nutrition field (ie, as mentioned in Lesson 2 many people misreport the number of calories they consume). While these two criticisms are valid, I do not believe either invalidates the findings of this study.
Perhaps a more appropriate criticism would be the concern of confounding lifestyle variables for lifetime abstainers These lifestyle factors would be very difficult to control for and may considerably influence the outcomes regarding all-cause mortality.
Subsequent studies
After
A 2018 article looking at this same NHIS data (and also data from the VA) found the lowest risk of death when drinking ~3 times weekly in the NHIS data and 2-3 times weekly in the VA data, with increased risk when drinking 5+ days weekly.(Hartz, 2018) The prior study pooled all of light drinkers together but this study divided the alcohol consumption groups into narrower bins of intake. Of note both of these data sets had alcohol measured only once and used in-person surveys (previously shown to yield underreporting of alcohol intake relative to anonymous surveys).
Additionally in 2018, a large analysis using data from 2016 looking at alcohol use globally across a large variety of health outcomes concluded that the optimal level of intake when looking at all health conditions is 0 drinks daily, though they find similar results with 1 drink daily.(GBD, 2018) The only health conditions for which they found benefit of alcohol intake were ischemic heart disease and diabetes mellitus. For the majority of health outcomes they looked at they found increased risk at any level of alcohol intake.
Another large study came out in 2018 that looked at almost 600,000 current drinkers across 83 studies.(Wood, 2018a) Here the authors excluded abstainers due in part to the concerns noted above. Thus, they were attempting to examine for people who drink alcohol what level of intake is associated with best outcomes. Of interest, ~71,000 of these participants from 37 studies had repeat measures of alcohol consumption and they calculated a regression dilution ratio of 0.50 (see note below for an explanation; similar to above this is a somewhat complicated concept and also is not necessary to understand the main points of the analysis).
Note: Regression dilution bias
By using repeat measurements over time, one can estimate the strength of this regression dilution, and then this can be applied as a correction factor.(Clarke, 1999) So, given a regression dilution ratio of 0.50, this implies that the regression coefficient relating health outcomes to baseline alcohol intake is ~1/2 the corrected regression coefficient relating health outcomes to alcohol intake throughout the study duration. Thus, the associations may be ~2x as strong as what studies that only consider baseline measurements show.
They found the lowest risk of all-cause mortality as well as CHD (not including myocardial infarction) with alcohol intake <100 grams weekly. The mean intake for the <100g intake group was 56 grams weekly (4 standard drinks). They found blood pressure and HDL increased with increasing alcohol consumption. For any given weekly alcohol intake they saw worse outcomes in people who drank less frequently (thus implying more potential binging). One commentary on this study noted that there were not worse numbers when drinking up to 200g weekly (14 standard drinks) in individuals who spread this out to 3+ days weekly.(Thompson, 2018) The original authors caution in a response that <50% of the recorded deaths had drinking frequency information and there were wide confidence intervals when attempting to examine the hazard ratio for association of binge drinking & disease outcomes, implying they do not have a complete enough data set to conclusively support that observation.(Wood, 2018b)
A more recent publication used data from the Health and Retirement Study that examined elderly individuals over 15 years, separated lifetime abstainers from former drinkers, took measures of alcohol intake every 2 years (one of the few studies with repeat measurements), and considered many confounders.(Keyes, 2019) They found that occasional and low level of alcohol intake had a hazard ratio of 0.81-0.93 for all-cause mortality relative to abstention. However, they also did not find an increased risk for heavy drinkers, which is not what has typically been seen previously; they attribute this to possible errors with self-report or reverse causation where people who are unhealthy decrease their alcohol intake. It is unclear to what degree this calls into question the overall results of the study.
Large randomized trial?
It is clear that some studies fin
Source of alcohol
Overall
Conclusion
So
With the documented risk that initiating alcohol consumption may lead to progressively heavier consumption, and no overwhelming evidence of a net benefit at low intake levels, I agree with the authors of most of the reviews and the dietary guidelines listed above that alcohol intake should be kept at a low volume of intake for people who do consume alcohol, binging should be avoided, and people who abstain should not be encouraged to begin consuming alcohol. For people who exercise binging should particularly be avoided around the timing of exercise sessions, and for people dieting if alcohol consumption triggers greater caloric intake then this should be minimize if possible.
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References
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