• Claire Sutcliffe

Spilling The Beans On Coffee

Updated: Mar 28

A regular black coffee contains two calories and a typical espresso contains only one calorie. So how can it make you gain weight?

Firstly, it’s complicated because everyone is different and scientific research has limitations. The effects of coffee change depending on whether you eat or not, your lifestyle, general health, race, and genetics. So while nutrition research gives you some clues, the most important thing to consider is your personal experience.

I started to drink coffee when I left home aged eighteen. I was studying business studies at the University of Birmingham. It was a demanding course and I desperately wanted to do well. Sometimes I was so tired from studying, late nights socializing, my poor diet and excessive alcohol consumption that I’d fall asleep in the library stacks while I was reading.

A girlfriend told me how she drank coffee to study until 2 am. This might not seem like a revelation nowadays with coffee chains everywhere and shops that sell energy drinks. But in the eighties, coffee was mostly of the instant kind, so I bought some, added sugar and milk to mask the bitter taste and drank it in the afternoon when I started to feel sleepy. It worked. Instead of going to bed at 10 pm, I was able to stay up until midnight. I was more tired in the morning because I was getting less sleep, so I also started to drink coffee as soon as I woke up. That term, I quickly put on lots of weight.

As a dietitian, looking back I can understand what happened. Coffee affects metabolism and neurotransmitters (messengers in the brain) so stress + coffee + sugar + a sedentary life creates a perfect storm for weight gain.

Caffeine blocks a hormone called adenosine – the sleep hormone that informs your brain that it’s time to take a nap. It raises adrenalin and epinephrine – the stress hormones that make you feel alert and ready-for-action. And it increases feel-good dopamine and helps us take up more serotonin so it acts like an anti-depressant. That’s why coffee is so enjoyable.

Adrenalin keeps your blood sugar raised so you have enough energy to react, but an elevated blood sugar can cause weight gain. Adenosine blocks insulin, so you can’t clear the sugar from your blood. If you drink coffee on an empty stomach your blood sugar will drop after two hours leaving you feeling tired and hungry and in need of another cup of coffee and a snack – extra calories mean extra weight.

That's exactly what I did. I probably ate an extra 300 calories from biscuits as I sipped sugary coffee. But biscuits have too much fat and sugar, and too little fiber and protein to stabilize blood sugar. As a result, I felt hungry all the time. But my hunger didn't seek a salad for lunch. My blood sugar was so wobbly, I craved quick fixes - toast, sandwiches, and snack food. It also made me too tired to exercise even though that would have helped to re-balance my hormones and blood sugar.

Years later, I still turn to coffee as a pick me up when I feel stressed and tired and often gain a few pounds. But now I know what's going on so see it as a red flag to rest more.

To understand coffee’s impact on your health you have to consider the research and how your body feels when you drink coffee. Your genes affect how you quickly you clear caffeine from your body - somewhere between 4-24 hours. Smokers metabolize it more quickly, while women taking the pill or HRT metabolize caffeine more slowly. If it affects your sleep and then your weight, like me, you are probably a slow metabolize. Here's what some of the research says:

  • Caffeine late in the day makes it harder for you to fall asleep and gives you poorer quality sleep. Poor quality sleep can affect your concentration and mood for up to four days.

  • Caffeine raises cortisol, blood sugar and causes insulin resistance (think of your muscles as lock and insulin as the key and insulin resistance when the key gets stuck). All this makes you put on belly fat.

  • Too much caffeine can make you jittery, overwhelmed, anxious, and irritable. You feel tired but wired.

  • You might get frequent colds. If you keep putting your body in a state of stress, you'll lower your immunity and increase inflammation.

  • The chlorogenic acid in coffee might make you rush to the loo. When your digestion is speeded up, you are not absorbing all the nutrients in your food. Furthermore, caffeine blocks iron absorption and uses up your B6. You may notice this in bloodwork.

  • Caffeine can trigger aura migraines and acid reflux.

  • Pregnant women must avoid all caffeine as it increases the risk of miscarriage.

  • People with coeliac may need to choose their coffee wisely as some instant coffee is contaminated with gluten. Even gluten-free coffee may attack your immune system because it has a similar molecular structure to gluten. This process is called molecular mimicry.

  • Women who are Asian, or going through menopause may have an even harder time metabolizing caffeine and it might interfere with their ability to metabolize bad estrogen which is linked to breast and ovarian cancer.

So if coffee’s so bad, why do I still drink it?

Although it impacts my sleep, coffee still has a number of benefits. I love the taste, short-term energy boost, and feel-good hormones. It’s a social drink, so when my friends have coffee I order one too because I’m a bit of a lemming. And coffee has other health benefits:

  • Improves endurance as it stimulates acetylcholine and muscle contractions, which makes the gym more pleasurable.

  • Improves brain power, alertness, logical reasoning, and memory.

  • Can lower the risk of heart disease and type 2 diabetes as it’s full of anti-oxidants as long as it doesn't raise your blood sugar which can increase your risk of diabetes.

  • Coffee contains nutrients like potassium, niacin, and magnesium. And the chlorogenic acid that makes you go to the loo helps to reduce your risk of colon cancer.

  • Reduces the risk of Parkinson’s, Alzheimer's and dementia because it improves circulation and neurotransmitters in the brain, especially if you are male. The benefit for women varies because estrogen gets in the way.

  • May lower the risk of breast and ovarian cancers in some women. Caucasian women who drink coffee may have lower estrogen as caffeine speeds up estrogen metabolism in the liver. But Asian women who drink coffee don't seem to get this benefit. All women regardless of race can benefit from the caffeine in cola and green tea as they both seem to increase good estrogen – estradiol.

  • Coffee can help certain auto-immune conditions that are caused by T-cell dominance like Hashimoto's, type 1 diabetes, and multiple sclerosis. Red wine (resveratrol), cooked tomatoes (lycopene), and aspirin (salicylate) also increase B-Cell activity to balance the T-cell immune response.

The caffeine content of common drinks in milligrams


Starbucks tall coffee (12 oz) 375

Instant coffee (8oz) 95

Brewed coffee (8oz) 60-180

Coffee ice cream (1 cup) 58

Starbucks espresso (1 oz) 35

Starbucks tall latte (12 oz) 35

Average Decaf coffee (1 cup) 5-10


Average Iced tea (8 oz) 47

Average green tea (8 oz) 30

Kombucha (8oz) 24

Herbal tea 0


Hot chocolate (8oz) 3-32

Cocoa powder (I tbsp) 12

Extra dark chocolate 30-210


Excedrin (2 tablets) 130

Soft drinks

Red bull (8.3 oz) 80

Mountain dew (12 oz) 56

Diet coke (12 oz) 47

Pepsi (12 oz) 38

Coca Cola (12 oz) 35

So what should you do?

  • Get to know your body. How does coffee make you feel? Are you anxious? Stressed? Then give up coffee for a week and see how you sleep. Re-introduce it after meals before trying it on an empty stomach. Instead of adding sugar try crushed cardamom pods or cinnamon to lower blood sugar and cortisol.

  • Know your threshold. 200 milligrams of caffeine will affect your blood sugar (100mg if you are a teenager). If you feel less hungry without coffee, switch to decaf as it only has a tiny effect on your blood sugar and insulin.

  • If you are Asian or have a history of estrogen dominant cancers you might like to quit coffee or limit yourself to one cup a day and drink green tea.

  • You might benefit from drinking coffee if you have type 1 diabetes, Hashimoto's or other TH1 dominant autoimmune diseases.

  • Skip the energy drinks no matter how tired you are. Caffeine toxicity accidentally kills people all the time.

For more information: Caffeine: Cognitive and Physical Performance Enhancer or Psychoactive Drug? Curr Neuropharmacol. 2015 Jan; 13(1): 71–88https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4462044/

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