We have limited data sources on the lives of ordinary people in Africa from before  colonialism, the sort of detailed archival research that historians have carried out in recent decades in to the histories of countries like the UK or Japan are only just starting in Africa. But there is evidence from oral history of pre-colonial famines in places like Tanzania (see Koponen, 1988), associated with drought. In the 19th century, in Tanzania, there's evidence of two general and severe periods of famine in the 1830s and 1860s, before German colonists entered the area in the 1880s. Koponen also has found references to two late 18th-century or early 19th-century famines on the southern coast of Tanzania. Meier (2006) discusses droughts and epidemics in pre-colonial Sudanic Africa, unfortunately I don't have access to more than the abstract.

Aside from these limited sources, we also know that famines were a sadly common feature of life around the world in pre-industrial times, including in countries that were colonial powers themselves. The first country to see a disappearance of peacetime famines was the Netherlands in the 1590s, followed by England in the 1620s.  The last famine in France was in 1788, just before the French Revolution, and in Spain in 1904-05. Even some countries known today as examples of prosperity, high levels of social trust and cohesiveness saw famines as late as the 19th century. For Japan, there are records (albeit with some gaps) of famines going back to the 6th century CE. Before the 1550s, Japan appears to have had more than 10 famines every 50 years on average. The last famine in Japan was 1833-1837. In Europe, Sweden and Finland's last famine was in 1867-69.  (Note that these recorded famines didn't necessarily affect the entire country, e.g. the Sweden and Finnish famine of 1867-69 was more about the northern parts of those countries. Also this leaves out famines caused by WWI or WWII in those countries, such as the Dutch "Hungry Winter" of 1944-45.)

Therefore it seems likely that there were famines and malnutrition in Africa long before imperialism. On the other hand, the persistence of those famines well into the 20th century is in all likelihood due to the poverty and political instability caused by imperialism (see Acemoğlu, Robinson, 2017).  There is ample evidence connecting European colonial activities in Africa with bad social and economic outcomes: the sub-Saharan African economic exception of Botswana is the country that was very lightly colonised, comparatively. Apart from the direct impacts of colonialism, newly independent countries often turned to socialist ideas, as in Tanzania and Ethiopia, presumably motivated at least in part by rejection of the liberal ideas of their ex-colonial rulers, meaning further disruptions to existing social and agricultural systems.

These disruptions matter for food security not just through their impact on GDP, as the Indian economist and Nobel Prize Winner, Amaryta Sen, observed, avoiding famine is as much about inclusive social institutions which redistribute to the poor as the food supply per se. The disappearance of famine in the Netherlands and England is attributed to both improved agricultural techniques and social redistribution via the Poor Laws in England and more informal charity in the Netherlands. These systems were badly disrupted by colonialism, and before that, by the Atlantic slave trade.

In line with Sen's work, Kopenen (1988) notes descriptions of various relief measures in pre-colonial Tanzania to handle famine, for example, a chief Mkwawa was reported by missionaries as organising food redistribution so well that "in an area as large as varied in that which he rules, it is virtually certain that famine never affected all parts of the chiefdom at the same time." He also notes differences in crops, and the farming systems around them that aim to reduce the likelihood of a total crop failure, rather than maximise output for any given year.

Kopenen also argues that European colonialism was and imperialism increasing food insecurity in Tanzania well before the start of actual colonialisation in the 1880s, through factors like:

• Increased warfare caused by the slave trade and associated raiding, which didn't just directly impact food production, but disrupted social institutions and allowed diseases to spread more rapidly.

• The adoption of maize, a crop from Mexico, in some farming in Tanzania, so local farmers had limited experience in handling its variations (as per the earlier point about avoiding crop failures rather than maximising agricultural output)

• Introduction of cattle diseases such as contagious bovine pleuropneumonia.

Imperialism, colonialism, and their flow on impacts have cost millions of lives. 

If it is any consolation, though, our worldindata has an article about life expectancy, including evidence that since the end of colonialism, life expectancies have improved in Africa, since 1920 African life expectancy at birth has doubled, from 26 years to 63 years.

Sources

Daron Acemoğlu, James Robinson 30 January 2017, The economic impact of colonialism,https://voxeu.org/article/economic-impact-colonialism

Joe Hasell (2013) - "Famines". Published online at OurWorldInData.org. Retrieved from: 'https://ourworldindata.org/famines' [Online Resource]

Koponen, J. (1988). War, Famine, and Pestilence in Late Precolonial Tanzania: A Case for a Heightened Mortality. The International Journal of African Historical Studies, 21(4), 637-676. doi:10.2307/219745

Meier, A. (2006). Natural Disasters? Droughts and Epidemics in Pre-colonial Sudanic Africa. The Medieval History Journal, 10(1–2), 209–236. https://doi.org/10.1177/097194580701000208